This is /home/pdm/install/Python-2.1/Doc/lib/python-lib.info, produced by makeinfo version 4.0 from lib.texi. April 15, 2001 2.1  File: python-lib.info, Node: Built-in Functions, Prev: Built-in Exceptions, Up: Built-in Objects Built-in Functions ================== The Python interpreter has a number of functions built into it that are always available. They are listed here in alphabetical order. `__import__(name[, globals[, locals[, fromlist]]])' This function is invoked by the `import' statement. It mainly exists so that you can replace it with another function that has a compatible interface, in order to change the semantics of the `import' statement. For examples of why and how you would do this, see the standard library modules `ihooks' and `rexec'. See also the built-in module `imp', which defines some useful operations out of which you can build your own `__import__()' function. For example, the statement `import spam' results in the following call: `__import__('spam',' `globals(),' `locals(), [])'; the statement `from spam.ham import eggs' results in `__import__('spam.ham', globals(), locals(), ['eggs'])'. Note that even though `locals()' and `['eggs']' are passed in as arguments, the `__import__()' function does not set the local variable named `eggs'; this is done by subsequent code that is generated for the import statement. (In fact, the standard implementation does not use its LOCALS argument at all, and uses its GLOBALS only to determine the package context of the `import' statement.) When the NAME variable is of the form `package.module', normally, the top-level package (the name up till the first dot) is returned, _not_ the module named by NAME. However, when a non-empty FROMLIST argument is given, the module named by NAME is returned. This is done for compatibility with the bytecode generated for the different kinds of import statement; when using `import spam.ham.eggs', the top-level package `spam' must be placed in the importing namespace, but when using `from spam.ham import eggs', the `spam.ham' subpackage must be used to find the `eggs' variable. As a workaround for this behavior, use `getattr()' to extract the desired components. For example, you could define the following helper: import string def my_import(name): mod = __import__(name) components = string.split(name, '.') for comp in components[1:]: mod = getattr(mod, comp) return mod `abs(x)' Return the absolute value of a number. The argument may be a plain or long integer or a floating point number. If the argument is a complex number, its magnitude is returned. `apply(function, args[, keywords])' The FUNCTION argument must be a callable object (a user-defined or built-in function or method, or a class object) and the ARGS argument must be a sequence (if it is not a tuple, the sequence is first converted to a tuple). The FUNCTION is called with ARGS as the argument list; the number of arguments is the the length of the tuple. (This is different from just calling `FUNC(ARGS)', since in that case there is always exactly one argument.) If the optional KEYWORDS argument is present, it must be a dictionary whose keys are strings. It specifies keyword arguments to be added to the end of the the argument list. `buffer(object[, offset[, size]])' The OBJECT argument must be an object that supports the buffer call interface (such as strings, arrays, and buffers). A new buffer object will be created which references the OBJECT argument. The buffer object will be a slice from the beginning of OBJECT (or from the specified OFFSET). The slice will extend to the end of OBJECT (or will have a length given by the SIZE argument). `callable(object)' Return true if the OBJECT argument appears callable, false if not. If this returns true, it is still possible that a call fails, but if it is false, calling OBJECT will never succeed. Note that classes are callable (calling a class returns a new instance); class instances are callable if they have a `__call__()' method. `chr(i)' Return a string of one character whose ASCII code is the integer I, e.g., `chr(97)' returns the string `'a''. This is the inverse of `ord()'. The argument must be in the range [0..255], inclusive; `ValueError' will be raised if I is outside that range. `cmp(x, y)' Compare the two objects X and Y and return an integer according to the outcome. The return value is negative if `X < Y', zero if `X == Y' and strictly positive if `X > Y'. `coerce(x, y)' Return a tuple consisting of the two numeric arguments converted to a common type, using the same rules as used by arithmetic operations. `compile(string, filename, kind)' Compile the STRING into a code object. Code objects can be executed by an `exec' statement or evaluated by a call to `eval()'. The FILENAME argument should give the file from which the code was read; pass e.g. `''' if it wasn't read from a file. The KIND argument specifies what kind of code must be compiled; it can be `'exec'' if STRING consists of a sequence of statements, `'eval'' if it consists of a single expression, or `'single'' if it consists of a single interactive statement (in the latter case, expression statements that evaluate to something else than `None' will printed). `complex(real[, imag])' Create a complex number with the value REAL + IMAG*j or convert a string or number to a complex number. Each argument may be any numeric type (including complex). If IMAG is omitted, it defaults to zero and the function serves as a numeric conversion function like `int()', `long()' and `float()'; in this case it also accepts a string argument which should be a valid complex number. `delattr(object, name)' This is a relative of `setattr()'. The arguments are an object and a string. The string must be the name of one of the object's attributes. The function deletes the named attribute, provided the object allows it. For example, `delattr(X, 'FOOBAR')' is equivalent to `del X.FOOBAR'. `dir([object])' Without arguments, return the list of names in the current local symbol table. With an argument, attempts to return a list of valid attribute for that object. This information is gleaned from the object's `__dict__', `__methods__' and `__members__' attributes, if defined. The list is not necessarily complete; e.g., for classes, attributes defined in base classes are not included, and for class instances, methods are not included. The resulting list is sorted alphabetically. For example: >>> import sys >>> dir() ['sys'] >>> dir(sys) ['argv', 'exit', 'modules', 'path', 'stderr', 'stdin', 'stdout'] `divmod(a, b)' Take two numbers as arguments and return a pair of numbers consisting of their quotient and remainder when using long division. With mixed operand types, the rules for binary arithmetic operators apply. For plain and long integers, the result is the same as `(A / B, A %{} B)'. For floating point numbers the result is `(Q, A %{} B)', where Q is usually `math.floor(A / B)' but may be 1 less than that. In any case `Q * B + A %{} B' is very close to A, if `A %{} B' is non-zero it has the same sign as B, and `0 <= abs(A %{} B) < abs(B)'. `eval(expression[, globals[, locals]])' The arguments are a string and two optional dictionaries. The EXPRESSION argument is parsed and evaluated as a Python expression (technically speaking, a condition list) using the GLOBALS and LOCALS dictionaries as global and local name space. If the LOCALS dictionary is omitted it defaults to the GLOBALS dictionary. If both dictionaries are omitted, the expression is executed in the environment where `eval' is called. The return value is the result of the evaluated expression. Syntax errors are reported as exceptions. Example: >>> x = 1 >>> print eval('x+1') 2 This function can also be used to execute arbitrary code objects (e.g. created by `compile()'). In this case pass a code object instead of a string. The code object must have been compiled passing `'eval'' to the KIND argument. Hints: dynamic execution of statements is supported by the `exec' statement. Execution of statements from a file is supported by the `execfile()' function. The `globals()' and `locals()' functions returns the current global and local dictionary, respectively, which may be useful to pass around for use by `eval()' or `execfile()'. `execfile(file[, globals[, locals]])' This function is similar to the `exec' statement, but parses a file instead of a string. It is different from the `import' statement in that it does not use the module administration -- it reads the file unconditionally and does not create a new module.(1) The arguments are a file name and two optional dictionaries. The file is parsed and evaluated as a sequence of Python statements (similarly to a module) using the GLOBALS and LOCALS dictionaries as global and local namespace. If the LOCALS dictionary is omitted it defaults to the GLOBALS dictionary. If both dictionaries are omitted, the expression is executed in the environment where `execfile()' is called. The return value is `None'. `filter(function, list)' Construct a list from those elements of LIST for which FUNCTION returns true. If LIST is a string or a tuple, the result also has that type; otherwise it is always a list. If FUNCTION is `None', the identity function is assumed, i.e. all elements of LIST that are false (zero or empty) are removed. `float(x)' Convert a string or a number to floating point. If the argument is a string, it must contain a possibly signed decimal or floating point number, possibly embedded in whitespace; this behaves identical to `string.atof(X)'. Otherwise, the argument may be a plain or long integer or a floating point number, and a floating point number with the same value (within Python's floating point precision) is returned. *Note:* When passing in a string, values for NaNand Infinity may be returned, depending on the underlying C library. The specific set of strings accepted which cause these values to be returned depends entirely on the C library and is known to vary. `getattr(object, name[, default])' Return the value of the named attributed of OBJECT. NAME must be a string. If the string is the name of one of the object's attributes, the result is the value of that attribute. For example, `getattr(x, 'foobar')' is equivalent to `x.foobar'. If the named attribute does not exist, DEFAULT is returned if provided, otherwise `AttributeError' is raised. `globals()' Return a dictionary representing the current global symbol table. This is always the dictionary of the current module (inside a function or method, this is the module where it is defined, not the module from which it is called). `hasattr(object, name)' The arguments are an object and a string. The result is 1 if the string is the name of one of the object's attributes, 0 if not. (This is implemented by calling `getattr(OBJECT, NAME)' and seeing whether it raises an exception or not.) `hash(object)' Return the hash value of the object (if it has one). Hash values are integers. They are used to quickly compare dictionary keys during a dictionary lookup. Numeric values that compare equal have the same hash value (even if they are of different types, e.g. 1 and 1.0). `hex(x)' Convert an integer number (of any size) to a hexadecimal string. The result is a valid Python expression. Note: this always yields an unsigned literal, e.g. on a 32-bit machine, `hex(-1)' yields `'0xffffffff''. When evaluated on a machine with the same word size, this literal is evaluated as -1; at a different word size, it may turn up as a large positive number or raise an `OverflowError' exception. `id(object)' Return the `identity' of an object. This is an integer (or long integer) which is guaranteed to be unique and constant for this object during its lifetime. Two objects whose lifetimes are disjunct may have the same `id()' value. (Implementation note: this is the address of the object.) `input([prompt])' Equivalent to `eval(raw_input(PROMPT))'. *Warning:* This function is not safe from user errors! It expects a valid Python expression as input; if the input is not syntactically valid, a `SyntaxError' will be raised. Other exceptions may be raised if there is an error during evaluation. (On the other hand, sometimes this is exactly what you need when writing a quick script for expert use.) If the `readline' module was loaded, then `input()' will use it to provide elaborate line editing and history features. Consider using the `raw_input()' function for general input from users. `int(x[, radix])' Convert a string or number to a plain integer. If the argument is a string, it must contain a possibly signed decimal number representable as a Python integer, possibly embedded in whitespace; this behaves identical to `string.atoi(X[, RADIX])'. The RADIX parameter gives the base for the conversion and may be any integer in the range [2, 36], or zero. If RADIX is zero, the proper radix is guessed based on the contents of string; the interpretation is the same as for integer literals. If RADIX is specified and X is not a string, `TypeError' is raised. Otherwise, the argument may be a plain or long integer or a floating point number. Conversion of floating point numbers to integers is defined by the C semantics; normally the conversion truncates towards zero.(2) `intern(string)' Enter STRING in the table of "interned" strings and return the interned string - which is STRING itself or a copy. Interning strings is useful to gain a little performance on dictionary lookup - if the keys in a dictionary are interned, and the lookup key is interned, the key comparisons (after hashing) can be done by a pointer compare instead of a string compare. Normally, the names used in Python programs are automatically interned, and the dictionaries used to hold module, class or instance attributes have interned keys. Interned strings are immortal (i.e. never get garbage collected). `isinstance(object, class)' Return true if the OBJECT argument is an instance of the CLASS argument, or of a (direct or indirect) subclass thereof. Also return true if CLASS is a type object and OBJECT is an object of that type. If OBJECT is not a class instance or a object of the given type, the function always returns false. If CLASS is neither a class object nor a type object, a `TypeError' exception is raised. `issubclass(class1, class2)' Return true if CLASS1 is a subclass (direct or indirect) of CLASS2. A class is considered a subclass of itself. If either argument is not a class object, a `TypeError' exception is raised. `len(s)' Return the length (the number of items) of an object. The argument may be a sequence (string, tuple or list) or a mapping (dictionary). `list(sequence)' Return a list whose items are the same and in the same order as SEQUENCE's items. If SEQUENCE is already a list, a copy is made and returned, similar to `SEQUENCE[:]'. For instance, `list('abc')' returns returns `['a', 'b', 'c']' and `list( (1, 2, 3) )' returns `[1, 2, 3]'. `locals()' Return a dictionary representing the current local symbol table. *Warning:* The contents of this dictionary should not be modified; changes may not affect the values of local variables used by the interpreter. `long(x[, radix])' Convert a string or number to a long integer. If the argument is a string, it must contain a possibly signed number of arbitrary size, possibly embedded in whitespace; this behaves identical to `string.atol(X)'. The RADIX argument is interpreted in the same way as for `int()', and may only be given when X is a string. Otherwise, the argument may be a plain or long integer or a floating point number, and a long integer with the same value is returned. Conversion of floating point numbers to integers is defined by the C semantics; see the description of `int()'. `map(function, list, ...)' Apply FUNCTION to every item of LIST and return a list of the results. If additional LIST arguments are passed, FUNCTION must take that many arguments and is applied to the items of all lists in parallel; if a list is shorter than another it is assumed to be extended with `None' items. If FUNCTION is `None', the identity function is assumed; if there are multiple list arguments, `map()' returns a list consisting of tuples containing the corresponding items from all lists (i.e. a kind of transpose operation). The LIST arguments may be any kind of sequence; the result is always a list. `max(s[, args...])' With a single argument S, return the largest item of a non-empty sequence (e.g., a string, tuple or list). With more than one argument, return the largest of the arguments. `min(s[, args...])' With a single argument S, return the smallest item of a non-empty sequence (e.g., a string, tuple or list). With more than one argument, return the smallest of the arguments. `oct(x)' Convert an integer number (of any size) to an octal string. The result is a valid Python expression. Note: this always yields an unsigned literal, e.g. on a 32-bit machine, `oct(-1)' yields `'037777777777''. When evaluated on a machine with the same word size, this literal is evaluated as -1; at a different word size, it may turn up as a large positive number or raise an `OverflowError' exception. `open(filename[, mode[, bufsize]])' Return a new file object (described earlier under Built-in Types). The first two arguments are the same as for `stdio''s `fopen()': FILENAME is the file name to be opened, MODE indicates how the file is to be opened: `'r'' for reading, `'w'' for writing (truncating an existing file), and `'a'' opens it for appending (which on _some_ UNIX systems means that _all_ writes append to the end of the file, regardless of the current seek position). Modes `'r+'', `'w+'' and `'a+'' open the file for updating (note that `'w+'' truncates the file). Append `'b'' to the mode to open the file in binary mode, on systems that differentiate between binary and text files (else it is ignored). If the file cannot be opened, `IOError' is raised. If MODE is omitted, it defaults to `'r''. When opening a binary file, you should append `'b'' to the MODE value for improved portability. (It's useful even on systems which don't treat binary and text files differently, where it serves as documentation.) The optional BUFSIZE argument specifies the file's desired buffer size: 0 means unbuffered, 1 means line buffered, any other positive value means use a buffer of (approximately) that size. A negative BUFSIZE means to use the system default, which is usually line buffered for for tty devices and fully buffered for other files. If omitted, the system default is used.(3) `ord(c)' Return the ASCII value of a string of one character or a Unicode character. E.g., `ord('a')' returns the integer `97', `ord(u'\u2020')' returns `8224'. This is the inverse of `chr()' for strings and of `unichr()' for Unicode characters. `pow(x, y[, z])' Return X to the power Y; if Z is present, return X to the power Y, modulo Z (computed more efficiently than `pow(X, Y) % Z'). The arguments must have numeric types. With mixed operand types, the rules for binary arithmetic operators apply. The effective operand type is also the type of the result; if the result is not expressible in this type, the function raises an exception; e.g., `pow(2, -1)' or `pow(2, 35000)' is not allowed. `range([start,] stop[, step])' This is a versatile function to create lists containing arithmetic progressions. It is most often used in `for' loops. The arguments must be plain integers. If the STEP argument is omitted, it defaults to `1'. If the START argument is omitted, it defaults to `0'. The full form returns a list of plain integers `[START, START + STEP, START + 2 * STEP, ...]'. If STEP is positive, the last element is the largest `START + I * STEP' less than STOP; if STEP is negative, the last element is the largest `START + I * STEP' greater than STOP. STEP must not be zero (or else `ValueError' is raised). Example: >>> range(10) [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] >>> range(1, 11) [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] >>> range(0, 30, 5) [0, 5, 10, 15, 20, 25] >>> range(0, 10, 3) [0, 3, 6, 9] >>> range(0, -10, -1) [0, -1, -2, -3, -4, -5, -6, -7, -8, -9] >>> range(0) [] >>> range(1, 0) [] `raw_input([prompt])' If the PROMPT argument is present, it is written to standard output without a trailing newline. The function then reads a line from input, converts it to a string (stripping a trailing newline), and returns that. When `EOF' is read, `EOFError' is raised. Example: >>> s = raw_input('--> ') --> Monty Python's Flying Circus >>> s "Monty Python's Flying Circus" If the `readline' module was loaded, then `raw_input()' will use it to provide elaborate line editing and history features. `reduce(function, sequence[, initializer])' Apply FUNCTION of two arguments cumulatively to the items of SEQUENCE, from left to right, so as to reduce the sequence to a single value. For example, `reduce(lambda x, y: x+y, [1, 2, 3, 4, 5])' calculates `((((1+2)+3)+4)+5)'. If the optional INITIALIZER is present, it is placed before the items of the sequence in the calculation, and serves as a default when the sequence is empty. `reload(module)' Re-parse and re-initialize an already imported MODULE. The argument must be a module object, so it must have been successfully imported before. This is useful if you have edited the module source file using an external editor and want to try out the new version without leaving the Python interpreter. The return value is the module object (i.e. the same as the MODULE argument). There are a number of caveats: If a module is syntactically correct but its initialization fails, the first `import' statement for it does not bind its name locally, but does store a (partially initialized) module object in `sys.modules'. To reload the module you must first `import' it again (this will bind the name to the partially initialized module object) before you can `reload()' it. When a module is reloaded, its dictionary (containing the module's global variables) is retained. Redefinitions of names will override the old definitions, so this is generally not a problem. If the new version of a module does not define a name that was defined by the old version, the old definition remains. This feature can be used to the module's advantage if it maintains a global table or cache of objects -- with a `try' statement it can test for the table's presence and skip its initialization if desired. It is legal though generally not very useful to reload built-in or dynamically loaded modules, except for `sys', `__main__' and `__builtin__'. In many cases, however, extension modules are not designed to be initialized more than once, and may fail in arbitrary ways when reloaded. If a module imports objects from another module using `from' ... `import' ..., calling `reload()' for the other module does not redefine the objects imported from it -- one way around this is to re-execute the `from' statement, another is to use `import' and qualified names (MODULE.NAME) instead. If a module instantiates instances of a class, reloading the module that defines the class does not affect the method definitions of the instances -- they continue to use the old class definition. The same is true for derived classes. `repr(object)' Return a string containing a printable representation of an object. This is the same value yielded by conversions (reverse quotes). It is sometimes useful to be able to access this operation as an ordinary function. For many types, this function makes an attempt to return a string that would yield an object with the same value when passed to `eval()'. `round(x[, n])' Return the floating point value X rounded to N digits after the decimal point. If N is omitted, it defaults to zero. The result is a floating point number. Values are rounded to the closest multiple of 10 to the power minus N; if two multiples are equally close, rounding is done away from 0 (so e.g. `round(0.5)' is `1.0' and `round(-0.5)' is `-1.0'). `setattr(object, name, value)' This is the counterpart of `getattr()'. The arguments are an object, a string and an arbitrary value. The string may name an existing attribute or a new attribute. The function assigns the value to the attribute, provided the object allows it. For example, `setattr(X, 'FOOBAR', 123)' is equivalent to `X.FOOBAR = 123'. `slice([start,] stop[, step])' Return a slice object representing the set of indices specified by `range(START, STOP, STEP)'. The START and STEP arguments default to None. Slice objects have read-only data attributes `start', `stop' and `step' which merely return the argument values (or their default). They have no other explicit functionality; however they are used by Numerical Python and other third party extensions. Slice objects are also generated when extended indexing syntax is used, e.g. for `a[start:stop:step]' or `a[start:stop, i]'. `str(object)' Return a string containing a nicely printable representation of an object. For strings, this returns the string itself. The difference with `repr(OBJECT)' is that `str(OBJECT)' does not always attempt to return a string that is acceptable to `eval()'; its goal is to return a printable string. `tuple(sequence)' Return a tuple whose items are the same and in the same order as SEQUENCE's items. If SEQUENCE is already a tuple, it is returned unchanged. For instance, `tuple('abc')' returns returns `('a', 'b', 'c')' and `tuple([1, 2, 3])' returns `(1, 2, 3)'. `type(object)' Return the type of an OBJECT. The return value is a type object. The standard module `types' defines names for all built-in types. For instance: >>> import types >>> if type(x) == types.StringType: print "It's a string" `unichr(i)' Return the Unicode string of one character whose Unicode code is the integer I, e.g., `unichr(97)' returns the string `u'a''. This is the inverse of `ord()' for Unicode strings. The argument must be in the range [0..65535], inclusive. `ValueError' is raised otherwise. _Added in Python version 2.0_ `unicode(string[, encoding[, errors]])' Decodes STRING using the codec for ENCODING. Error handling is done according to ERRORS. The default behavior is to decode UTF-8 in strict mode, meaning that encoding errors raise `ValueError'. See also the `codecs' module. _Added in Python version 2.0_ `vars([object])' Without arguments, return a dictionary corresponding to the current local symbol table. With a module, class or class instance object as argument (or anything else that has a `__dict__' attribute), returns a dictionary corresponding to the object's symbol table. The returned dictionary should not be modified: the effects on the corresponding symbol table are undefined.(4) `xrange([start,] stop[, step])' This function is very similar to `range()', but returns an "xrange object" instead of a list. This is an opaque sequence type which yields the same values as the corresponding list, without actually storing them all simultaneously. The advantage of `xrange()' over `range()' is minimal (since `xrange()' still has to create the values when asked for them) except when a very large range is used on a memory-starved machine (e.g. MS-DOS) or when all of the range's elements are never used (e.g. when the loop is usually terminated with `break'). `zip(seq1, ...)' This function returns a list of tuples, where each tuple contains the I-th element from each of the argument sequences. At least one sequence is required, otherwise a `TypeError' is raised. The returned list is truncated in length to the length of the shortest argument sequence. When there are multiple argument sequences which are all of the same length, `zip()' is similar to `map()' with an initial argument of `None'. With a single sequence argument, it returns a list of 1-tuples. _Added in Python version 2.0_ ---------- Footnotes ---------- (1) It is used relatively rarely so does not warrant being made into a statement. (2) This is ugly -- the language definition should require truncation towards zero. (3) Specifying a buffer size currently has no effect on systems that don't have `setvbuf()'. The interface to specify the buffer size is not done using a method that calls `setvbuf()', because that may dump core when called after any I/O has been performed, and there's no reliable way to determine whether this is the case. (4) In the current implementation, local variable bindings cannot normally be affected this way, but variables retrieved from other scopes (e.g. modules) can be. This may change.  File: python-lib.info, Node: Python Runtime Services, Next: String Services, Prev: Built-in Objects, Up: Top Python Runtime Services *********************** The modules described in this chapter provide a wide range of services related to the Python interpreter and its interaction with its environment. Here's an overview: * Menu: * sys:: * gc:: * weakref:: * fpectl:: * atexit:: * types:: * UserDict:: * UserList:: * UserString:: * operator:: * inspect:: * traceback:: * linecache:: * pickle:: * cPickle:: * copy_reg:: * shelve:: * copy:: * marshal:: * warnings:: * imp:: * code:: * codeop:: * pprint:: * repr:: * new:: * site:: * user:: * __builtin__:: * __main__::  File: python-lib.info, Node: sys, Next: gc, Prev: Python Runtime Services, Up: Python Runtime Services System-specific parameters and functions ======================================== Access system-specific parameters and functions. This module provides access to some variables used or maintained by the interpreter and to functions that interact strongly with the interpreter. It is always available. `argv' The list of command line arguments passed to a Python script. `argv[0]' is the script name (it is operating system dependent whether this is a full pathname or not). If the command was executed using the `-c' command line option to the interpreter, `argv[0]' is set to the string `'-c''. If no script name was passed to the Python interpreter, `argv' has zero length. `byteorder' An indicator of the native byte order. This will have the value `'big'' on big-endian (most-signigicant byte first) platforms, and `'little'' on little-endian (least-significant byte first) platforms. _Added in Python version 2.0_ `builtin_module_names' A tuple of strings giving the names of all modules that are compiled into this Python interpreter. (This information is not available in any other way -- `modules.keys()' only lists the imported modules.) `copyright' A string containing the copyright pertaining to the Python interpreter. `dllhandle' Integer specifying the handle of the Python DLL. Availability: Windows. `displayhook(VALUE)' If VALUE is not `None', this function prints it to `sys.stdout', and saves it in `__builtin__._'. `sys.displayhook' is called on the result of evaluating an expression entered in an interactive Python session. The display of these values can be customized by assigning another one-argument function to `sys.displayhook'. `excepthook(TYPE, VALUE, TRACEBACK)' This function prints out a given traceback and exception to `sys.stderr'. When an exception is raised and uncaught, the interpreter calls `sys.excepthook' with three arguments, the exception class, exception instance, and a traceback object. In an interactive session this happens just before control is returned to the prompt; in a Python program this happens just before the program exits. The handling of such top-level exceptions can be customized by assigning another three-argument function to `sys.excepthook'. `__displayhook__' `__excepthook__' These objects contain the original values of `displayhook' and `excepthook' at the start of the program. They are saved so that `displayhook' and `excepthook' can be restored in case they happen to get replaced with broken objects. `exc_info()' This function returns a tuple of three values that give information about the exception that is currently being handled. The information returned is specific both to the current thread and to the current stack frame. If the current stack frame is not handling an exception, the information is taken from the calling stack frame, or its caller, and so on until a stack frame is found that is handling an exception. Here, "handling an exception" is defined as "executing or having executed an except clause." For any stack frame, only information about the most recently handled exception is accessible. If no exception is being handled anywhere on the stack, a tuple containing three `None' values is returned. Otherwise, the values returned are `(TYPE, VALUE, TRACEBACK)'. Their meaning is: TYPE gets the exception type of the exception being handled (a string or class object); VALUE gets the exception parameter (its "associated value" or the second argument to `raise', which is always a class instance if the exception type is a class object); TRACEBACK gets a traceback object (see the Reference Manual) which encapsulates the call stack at the point where the exception originally occurred. *Warning:* assigning the TRACEBACK return value to a local variable in a function that is handling an exception will cause a circular reference. This will prevent anything referenced by a local variable in the same function or by the traceback from being garbage collected. Since most functions don't need access to the traceback, the best solution is to use something like `type, value = sys.exc_info()[:2]' to extract only the exception type and value. If you do need the traceback, make sure to delete it after use (best done with a `try' ... `finally' statement) or to call `exc_info()' in a function that does not itself handle an exception. `exc_type' `exc_value' `exc_traceback' _This is deprecated in Python 1.5. Use `exc_info()' instead._ Since they are global variables, they are not specific to the current thread, so their use is not safe in a multi-threaded program. When no exception is being handled, `exc_type' is set to `None' and the other two are undefined. `exec_prefix' A string giving the site-specific directory prefix where the platform-dependent Python files are installed; by default, this is also `'/usr/local''. This can be set at build time with the `--exec-prefix' argument to the `configure' script. Specifically, all configuration files (e.g. the `config.h' header file) are installed in the directory `exec_prefix + '/lib/pythonVERSION/config'', and shared library modules are installed in `exec_prefix + '/lib/pythonVERSION/lib-dynload'', where VERSION is equal to `version[:3]'. `executable' A string giving the name of the executable binary for the Python interpreter, on systems where this makes sense. `exit([arg])' Exit from Python. This is implemented by raising the `SystemExit' exception, so cleanup actions specified by finally clauses of `try' statements are honored, and it is possible to intercept the exit attempt at an outer level. The optional argument ARG can be an integer giving the exit status (defaulting to zero), or another type of object. If it is an integer, zero is considered "successful termination" and any nonzero value is considered "abnormal termination" by shells and the like. Most systems require it to be in the range 0-127, and produce undefined results otherwise. Some systems have a convention for assigning specific meanings to specific exit codes, but these are generally underdeveloped; Unix programs generally use 2 for command line syntax errors and 1 for all other kind of errors. If another type of object is passed, `None' is equivalent to passing zero, and any other object is printed to `sys.stderr' and results in an exit code of 1. In particular, `sys.exit("some error message")' is a quick way to exit a program when an error occurs. `exitfunc' This value is not actually defined by the module, but can be set by the user (or by a program) to specify a clean-up action at program exit. When set, it should be a parameterless function. This function will be called when the interpreter exits. Only one function may be installed in this way; to allow multiple functions which will be called at termination, use the `atexit' module. Note: the exit function is not called when the program is killed by a signal, when a Python fatal internal error is detected, or when `os._exit()' is called. `getdefaultencoding()' Return the name of the current default string encoding used by the Unicode implementation. _Added in Python version 2.0_ `getrefcount(object)' Return the reference count of the OBJECT. The count returned is generally one higher than you might expect, because it includes the (temporary) reference as an argument to `getrefcount()'. `getrecursionlimit()' Return the current value of the recursion limit, the maximum depth of the Python interpreter stack. This limit prevents infinite recursion from causing an overflow of the C stack and crashing Python. It can be set by `setrecursionlimit()'. `_getframe([depth])' Return a frame object from the call stack. If optional integer DEPTH is given, return the frame object that many calls below the top of the stack. If that is deeper than the call stack, `ValueError' is raised. The default for DEPTH is zero, returning the frame at the top of the call stack. This function should be used for internal and specialized purposes only. `hexversion' The version number encoded as a single integer. This is guaranteed to increase with each version, including proper support for non-production releases. For example, to test that the Python interpreter is at least version 1.5.2, use: if sys.hexversion >= 0x010502F0: # use some advanced feature ... else: # use an alternative implementation or warn the user ... This is called `hexversion' since it only really looks meaningful when viewed as the result of passing it to the built-in `hex()' function. The `version_info' value may be used for a more human-friendly encoding of the same information. _Added in Python version 1.5.2_ `last_type' `last_value' `last_traceback' These three variables are not always defined; they are set when an exception is not handled and the interpreter prints an error message and a stack traceback. Their intended use is to allow an interactive user to import a debugger module and engage in post-mortem debugging without having to re-execute the command that caused the error. (Typical use is `import pdb; pdb.pm()' to enter the post-mortem debugger; see the chapter "The Python Debugger" for more information.) The meaning of the variables is the same as that of the return values from `exc_info()' above. (Since there is only one interactive thread, thread-safety is not a concern for these variables, unlike for `exc_type' etc.) `maxint' The largest positive integer supported by Python's regular integer type. This is at least 2**31-1. The largest negative integer is `-maxint-1' - the asymmetry results from the use of 2's complement binary arithmetic. `modules' This is a dictionary that maps module names to modules which have already been loaded. This can be manipulated to force reloading of modules and other tricks. Note that removing a module from this dictionary is _not_ the same as calling `reload()' on the corresponding module object. `path' A list of strings that specifies the search path for modules. Initialized from the environment variable `PYTHONPATH', or an installation-dependent default. The first item of this list, `path[0]', is the directory containing the script that was used to invoke the Python interpreter. If the script directory is not available (e.g. if the interpreter is invoked interactively or if the script is read from standard input), `path[0]' is the empty string, which directs Python to search modules in the current directory first. Notice that the script directory is inserted _before_ the entries inserted as a result of `PYTHONPATH'. `platform' This string contains a platform identifier, e.g. `'sunos5'' or `'linux1''. This can be used to append platform-specific components to `path', for instance. `prefix' A string giving the site-specific directory prefix where the platform independent Python files are installed; by default, this is the string `'/usr/local''. This can be set at build time with the `--prefix' argument to the `configure' script. The main collection of Python library modules is installed in the directory `prefix + '/lib/pythonVERSION'' while the platform independent header files (all except `config.h') are stored in `prefix + '/include/pythonVERSION'', where VERSION is equal to `version[:3]'. `ps1' `ps2' Strings specifying the primary and secondary prompt of the interpreter. These are only defined if the interpreter is in interactive mode. Their initial values in this case are `'>`>'> '' and `'... ''. If a non-string object is assigned to either variable, its `str()' is re-evaluated each time the interpreter prepares to read a new interactive command; this can be used to implement a dynamic prompt. `setcheckinterval(interval)' Set the interpreter's "check interval". This integer value determines how often the interpreter checks for periodic things such as thread switches and signal handlers. The default is `10', meaning the check is performed every 10 Python virtual instructions. Setting it to a larger value may increase performance for programs using threads. Setting it to a value `<=' 0 checks every virtual instruction, maximizing responsiveness as well as overhead. `setdefaultencoding(name)' Set the current default string encoding used by the Unicode implementation. If NAME does not match any available encoding, `LookupError' is raised. This function is only intended to be used by the `site' module implementation and, where needed, by `sitecustomize'. Once used by the `site' module, it is removed from the `sys' module's namespace. _Added in Python version 2.0_ `setprofile(profilefunc)' Set the system's profile function, which allows you to implement a Python source code profiler in Python. See the chapter on the Python Profiler. The system's profile function is called similarly to the system's trace function (see `settrace()'), but it isn't called for each executed line of code (only on call and return and when an exception occurs). Also, its return value is not used, so it can just return `None'. `setrecursionlimit(limit)' Set the maximum depth of the Python interpreter stack to LIMIT. This limit prevents infinite recursion from causing an overflow of the C stack and crashing Python. The highest possible limit is platform-dependent. A user may need to set the limit higher when she has a program that requires deep recursion and a platform that supports a higher limit. This should be done with care, because a too-high limit can lead to a crash. `settrace(tracefunc)' Set the system's trace function, which allows you to implement a Python source code debugger in Python. See section "How It Works" in the chapter on the Python Debugger. `stdin' `stdout' `stderr' File objects corresponding to the interpreter's standard input, output and error streams. `stdin' is used for all interpreter input except for scripts but including calls to `input()' and `raw_input()'. `stdout' is used for the output of `print' and expression statements and for the prompts of `input()' and `raw_input()'. The interpreter's own prompts and (almost all of) its error messages go to `stderr'. `stdout' and `stderr' needn't be built-in file objects: any object is acceptable as long as it has a `write()' method that takes a string argument. (Changing these objects doesn't affect the standard I/O streams of processes executed by `os.popen()', `os.system()' or the `exec*()' family of functions in the `os' module.) `__stdin__' `__stdout__' `__stderr__' These objects contain the original values of `stdin', `stderr' and `stdout' at the start of the program. They are used during finalization, and could be useful to restore the actual files to known working file objects in case they have been overwritten with a broken object. `tracebacklimit' When this variable is set to an integer value, it determines the maximum number of levels of traceback information printed when an unhandled exception occurs. The default is `1000'. When set to 0 or less, all traceback information is suppressed and only the exception type and value are printed. `version' A string containing the version number of the Python interpreter plus additional information on the build number and compiler used. It has a value of the form `'VERSION (#BUILD_NUMBER, BUILD_DATE, BUILD_TIME) [COMPILER]''. The first three characters are used to identify the version in the installation directories (where appropriate on each platform). An example: >>> import sys >>> sys.version '1.5.2 (#0 Apr 13 1999, 10:51:12) [MSC 32 bit (Intel)]' `version_info' A tuple containing the five components of the version number: MAJOR, MINOR, MICRO, RELEASELEVEL, and SERIAL. All values except RELEASELEVEL are integers; the release level is `'alpha'', `'beta'', `'candidate'', or `'final''. The `version_info' value corresponding to the Python version 2.0 is `(2, 0, 0, 'final', 0)'. _Added in Python version 2.0_ `winver' The version number used to form registry keys on Windows platforms. This is stored as string resource 1000 in the Python DLL. The value is normally the first three characters of `version'. It is provided in the `sys' module for informational purposes; modifying this value has no effect on the registry keys used by Python. Availability: Windows.