This function is invoked by the
importstatement. 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
ihooksand
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
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.
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.
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).
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.
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.
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.
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. '<string>'
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).
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.
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.
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:
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).
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().
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.2.8
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.
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.
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 NaN and Infinitymay 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.
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.
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).
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.)
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).
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.
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.)
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.
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.2.9
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).
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.
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.
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].
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.
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().
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.
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.
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.
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.
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.2.10
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.
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.
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:
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.
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.
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.
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().
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).
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.
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
Pythonand 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]".
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.
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).
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.
New in version 2.0.
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.
New in version 2.0.
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.2.11
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).
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.
New in version 2.0.
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.
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.