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abc.rst.txt	7219	0644	editdlrm
aepack.rst.txt	4257	0644	editdlrm
aetools.rst.txt	3532	0644	editdlrm
aetypes.rst.txt	4257	0644	editdlrm
aifc.rst.txt	7086	0644	editdlrm
al.rst.txt	5309	0644	editdlrm
allos.rst.txt	695	0644	editdlrm
anydbm.rst.txt	4111	0644	editdlrm
archiving.rst.txt	424	0644	editdlrm
argparse.rst.txt	74685	0644	editdlrm
array.rst.txt	10524	0644	editdlrm
ast.rst.txt	10111	0644	editdlrm
asynchat.rst.txt	9206	0644	editdlrm
asyncore.rst.txt	12937	0644	editdlrm
atexit.rst.txt	3910	0644	editdlrm
audioop.rst.txt	10395	0644	editdlrm
autogil.rst.txt	1015	0644	editdlrm
base64.rst.txt	6252	0644	editdlrm
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bdb.rst.txt	12456	0644	editdlrm
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bz2.rst.txt	8064	0644	editdlrm
calendar.rst.txt	11282	0644	editdlrm
carbon.rst.txt	15956	0644	editdlrm
cd.rst.txt	11974	0644	editdlrm
cgi.rst.txt	22853	0644	editdlrm
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code.rst.txt	7115	0644	editdlrm
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codeop.rst.txt	3774	0644	editdlrm
collections.rst.txt	41448	0644	editdlrm
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compileall.rst.txt	4678	0644	editdlrm
compiler.rst.txt	37464	0644	editdlrm
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crypt.rst.txt	2292	0644	editdlrm
crypto.rst.txt	355	0644	editdlrm
csv.rst.txt	22757	0644	editdlrm
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curses.ascii.rst.txt	9046	0644	editdlrm
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dbm.rst.txt	3117	0644	editdlrm
debug.rst.txt	446	0644	editdlrm
decimal.rst.txt	70926	0644	editdlrm
development.rst.txt	640	0644	editdlrm
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dl.rst.txt	3392	0644	editdlrm
doctest.rst.txt	73985	0644	editdlrm
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dummy_threading.rst.txt	799	0644	editdlrm
easydialogs.rst.txt	10346	0644	editdlrm
email-examples.rst.txt	1271	0644	editdlrm
email.charset.rst.txt	9654	0644	editdlrm
email.encoders.rst.txt	2376	0644	editdlrm
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ensurepip.rst.txt	5022	0644	editdlrm
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fcntl.rst.txt	7361	0644	editdlrm
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fileinput.rst.txt	7417	0644	editdlrm
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fl.rst.txt	17646	0644	editdlrm
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fnmatch.rst.txt	3104	0644	editdlrm
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fpectl.rst.txt	4171	0644	editdlrm
fpformat.rst.txt	1747	0644	editdlrm
fractions.rst.txt	5297	0644	editdlrm
framework.rst.txt	11444	0644	editdlrm
frameworks.rst.txt	378	0644	editdlrm
ftplib.rst.txt	15720	0644	editdlrm
functions.rst.txt	75554	0644	editdlrm
functools.rst.txt	7448	0644	editdlrm
future_builtins.rst.txt	2010	0644	editdlrm
gc.rst.txt	9014	0644	editdlrm
gdbm.rst.txt	4882	0644	editdlrm
gensuitemodule.rst.txt	3113	0644	editdlrm
getopt.rst.txt	6670	0644	editdlrm
getpass.rst.txt	1876	0644	editdlrm
gettext.rst.txt	29040	0644	editdlrm
gl.rst.txt	6009	0644	editdlrm
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hotshot.rst.txt	4289	0644	editdlrm
htmllib.rst.txt	7379	0644	editdlrm
htmlparser.rst.txt	11640	0644	editdlrm
httplib.rst.txt	37454	0644	editdlrm
i18n.rst.txt	409	0644	editdlrm
ic.rst.txt	5005	0644	editdlrm
idle.rst.txt	22182	0644	editdlrm
imageop.rst.txt	4001	0644	editdlrm
imaplib.rst.txt	17221	0644	editdlrm
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importlib.rst.txt	1126	0644	editdlrm
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index.rst.txt	2287	0644	editdlrm
inspect.rst.txt	28151	0644	editdlrm
internet.rst.txt	950	0644	editdlrm
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io.rst.txt	39015	0644	editdlrm
ipc.rst.txt	630	0644	editdlrm
itertools.rst.txt	36324	0644	editdlrm
jpeg.rst.txt	3858	0644	editdlrm
json.rst.txt	25545	0644	editdlrm
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logging.config.rst.txt	31560	0644	editdlrm
logging.handlers.rst.txt	28153	0644	editdlrm
logging.rst.txt	46882	0644	editdlrm
mac.rst.txt	791	0644	editdlrm
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mailbox.rst.txt	68129	0644	editdlrm
mailcap.rst.txt	3675	0644	editdlrm
markup.rst.txt	1249	0644	editdlrm
marshal.rst.txt	5689	0644	editdlrm
math.rst.txt	10920	0644	editdlrm
md5.rst.txt	2815	0644	editdlrm
mhlib.rst.txt	3966	0644	editdlrm
mimetools.rst.txt	4504	0644	editdlrm
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mimewriter.rst.txt	3360	0644	editdlrm
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mmap.rst.txt	10481	0644	editdlrm
modulefinder.rst.txt	3380	0644	editdlrm
modules.rst.txt	382	0644	editdlrm
msilib.rst.txt	19062	0644	editdlrm
msvcrt.rst.txt	4346	0644	editdlrm
multifile.rst.txt	6613	0644	editdlrm
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mutex.rst.txt	1939	0644	editdlrm
netdata.rst.txt	432	0644	editdlrm
netrc.rst.txt	3119	0644	editdlrm
new.rst.txt	2653	0644	editdlrm
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numbers.rst.txt	8007	0644	editdlrm
numeric.rst.txt	751	0644	editdlrm
operator.rst.txt	22092	0644	editdlrm
optparse.rst.txt	77101	0644	editdlrm
os.path.rst.txt	13094	0644	editdlrm
os.rst.txt	82580	0644	editdlrm
ossaudiodev.rst.txt	17309	0644	editdlrm
othergui.rst.txt	2721	0644	editdlrm
parser.rst.txt	15385	0644	editdlrm
pdb.rst.txt	16043	0644	editdlrm
persistence.rst.txt	826	0644	editdlrm
pickle.rst.txt	37262	0644	editdlrm
pickletools.rst.txt	1997	0644	editdlrm
pipes.rst.txt	3786	0644	editdlrm
pkgutil.rst.txt	7714	0644	editdlrm
platform.rst.txt	9554	0644	editdlrm
plistlib.rst.txt	4134	0644	editdlrm
popen2.rst.txt	7022	0644	editdlrm
poplib.rst.txt	6220	0644	editdlrm
posix.rst.txt	3630	0644	editdlrm
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pprint.rst.txt	9071	0644	editdlrm
profile.rst.txt	28666	0644	editdlrm
pty.rst.txt	1762	0644	editdlrm
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pyclbr.rst.txt	3296	0644	editdlrm
pydoc.rst.txt	4083	0644	editdlrm
pyexpat.rst.txt	28891	0644	editdlrm
python.rst.txt	514	0644	editdlrm
py_compile.rst.txt	2479	0644	editdlrm
queue.rst.txt	7034	0644	editdlrm
quopri.rst.txt	2670	0644	editdlrm
random.rst.txt	13319	0644	editdlrm
re.rst.txt	55102	0644	editdlrm
readline.rst.txt	10513	0644	editdlrm
repr.rst.txt	4718	0644	editdlrm
resource.rst.txt	9595	0644	editdlrm
restricted.rst.txt	3327	0644	editdlrm
rexec.rst.txt	11742	0644	editdlrm
rfc822.rst.txt	14037	0644	editdlrm
rlcompleter.rst.txt	2494	0644	editdlrm
robotparser.rst.txt	2190	0644	editdlrm
runpy.rst.txt	6938	0644	editdlrm
sched.rst.txt	4644	0644	editdlrm
scrolledtext.rst.txt	1379	0644	editdlrm
select.rst.txt	20705	0644	editdlrm
sets.rst.txt	14973	0644	editdlrm
sgi.rst.txt	322	0644	editdlrm
sgmllib.rst.txt	10664	0644	editdlrm
sha.rst.txt	2807	0644	editdlrm
shelve.rst.txt	8319	0644	editdlrm
shlex.rst.txt	11313	0644	editdlrm
shutil.rst.txt	13491	0644	editdlrm
signal.rst.txt	10719	0644	editdlrm
simplehttpserver.rst.txt	4559	0644	editdlrm
simplexmlrpcserver.rst.txt	10881	0644	editdlrm
site.rst.txt	7880	0644	editdlrm
smtpd.rst.txt	2464	0644	editdlrm
smtplib.rst.txt	14906	0644	editdlrm
sndhdr.rst.txt	1759	0644	editdlrm
socket.rst.txt	40765	0644	editdlrm
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someos.rst.txt	599	0644	editdlrm
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sqlite3.rst.txt	35448	0644	editdlrm
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string.rst.txt	44085	0644	editdlrm
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stringprep.rst.txt	4238	0644	editdlrm
strings.rst.txt	746	0644	editdlrm
struct.rst.txt	17100	0644	editdlrm
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xml.etree.elementtree.rst.txt	35707	0644	editdlrm
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xml.sax.utils.rst.txt	3560	0644	editdlrm
xmlrpclib.rst.txt	22559	0644	editdlrm
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__main__.rst.txt	535	0644	editdlrm

:mod:`ast` --- Abstract Syntax Trees ==================================== .. module:: ast :synopsis: Abstract Syntax Tree classes and manipulation. .. sectionauthor:: Martin v. Löwis .. sectionauthor:: Georg Brandl .. versionadded:: 2.5 The low-level ``_ast`` module containing only the node classes. .. versionadded:: 2.6 The high-level ``ast`` module containing all helpers. **Source code:** :source:`Lib/ast.py` -------------- The :mod:`ast` module helps Python applications to process trees of the Python abstract syntax grammar. The abstract syntax itself might change with each Python release; this module helps to find out programmatically what the current grammar looks like. An abstract syntax tree can be generated by passing :data:`ast.PyCF_ONLY_AST` as a flag to the :func:`compile` built-in function, or using the :func:`parse` helper provided in this module. The result will be a tree of objects whose classes all inherit from :class:`ast.AST`. An abstract syntax tree can be compiled into a Python code object using the built-in :func:`compile` function. Node classes ------------ .. class:: AST This is the base of all AST node classes. The actual node classes are derived from the :file:`Parser/Python.asdl` file, which is reproduced :ref:`below `. They are defined in the :mod:`_ast` C module and re-exported in :mod:`ast`. There is one class defined for each left-hand side symbol in the abstract grammar (for example, :class:`ast.stmt` or :class:`ast.expr`). In addition, there is one class defined for each constructor on the right-hand side; these classes inherit from the classes for the left-hand side trees. For example, :class:`ast.BinOp` inherits from :class:`ast.expr`. For production rules with alternatives (aka "sums"), the left-hand side class is abstract: only instances of specific constructor nodes are ever created. .. attribute:: _fields Each concrete class has an attribute :attr:`_fields` which gives the names of all child nodes. Each instance of a concrete class has one attribute for each child node, of the type as defined in the grammar. For example, :class:`ast.BinOp` instances have an attribute :attr:`left` of type :class:`ast.expr`. If these attributes are marked as optional in the grammar (using a question mark), the value might be ``None``. If the attributes can have zero-or-more values (marked with an asterisk), the values are represented as Python lists. All possible attributes must be present and have valid values when compiling an AST with :func:`compile`. .. attribute:: lineno col_offset Instances of :class:`ast.expr` and :class:`ast.stmt` subclasses have :attr:`lineno` and :attr:`col_offset` attributes. The :attr:`lineno` is the line number of source text (1-indexed so the first line is line 1) and the :attr:`col_offset` is the UTF-8 byte offset of the first token that generated the node. The UTF-8 offset is recorded because the parser uses UTF-8 internally. The constructor of a class :class:`ast.T` parses its arguments as follows: * If there are positional arguments, there must be as many as there are items in :attr:`T._fields`; they will be assigned as attributes of these names. * If there are keyword arguments, they will set the attributes of the same names to the given values. For example, to create and populate an :class:`ast.UnaryOp` node, you could use :: node = ast.UnaryOp() node.op = ast.USub() node.operand = ast.Num() node.operand.n = 5 node.operand.lineno = 0 node.operand.col_offset = 0 node.lineno = 0 node.col_offset = 0 or the more compact :: node = ast.UnaryOp(ast.USub(), ast.Num(5, lineno=0, col_offset=0), lineno=0, col_offset=0) .. versionadded:: 2.6 The constructor as explained above was added. In Python 2.5 nodes had to be created by calling the class constructor without arguments and setting the attributes afterwards. .. _abstract-grammar: Abstract Grammar ---------------- The module defines a string constant ``__version__`` which is the decimal Subversion revision number of the file shown below. The abstract grammar is currently defined as follows: .. literalinclude:: ../../Parser/Python.asdl :language: none :mod:`ast` Helpers ------------------ .. versionadded:: 2.6 Apart from the node classes, :mod:`ast` module defines these utility functions and classes for traversing abstract syntax trees: .. function:: parse(source, filename='', mode='exec') Parse the source into an AST node. Equivalent to ``compile(source, filename, mode, ast.PyCF_ONLY_AST)``. .. function:: literal_eval(node_or_string) Safely evaluate an expression node or a Unicode or *Latin-1* encoded string containing a Python literal or container display. The string or node provided may only consist of the following Python literal structures: strings, numbers, tuples, lists, dicts, booleans, and ``None``. This can be used for safely evaluating strings containing Python values from untrusted sources without the need to parse the values oneself. It is not capable of evaluating arbitrarily complex expressions, for example involving operators or indexing. .. function:: get_docstring(node, clean=True) Return the docstring of the given *node* (which must be a :class:`FunctionDef`, :class:`ClassDef` or :class:`Module` node), or ``None`` if it has no docstring. If *clean* is true, clean up the docstring's indentation with :func:`inspect.cleandoc`. .. function:: fix_missing_locations(node) When you compile a node tree with :func:`compile`, the compiler expects :attr:`lineno` and :attr:`col_offset` attributes for every node that supports them. This is rather tedious to fill in for generated nodes, so this helper adds these attributes recursively where not already set, by setting them to the values of the parent node. It works recursively starting at *node*. .. function:: increment_lineno(node, n=1) Increment the line number of each node in the tree starting at *node* by *n*. This is useful to "move code" to a different location in a file. .. function:: copy_location(new_node, old_node) Copy source location (:attr:`lineno` and :attr:`col_offset`) from *old_node* to *new_node* if possible, and return *new_node*. .. function:: iter_fields(node) Yield a tuple of ``(fieldname, value)`` for each field in ``node._fields`` that is present on *node*. .. function:: iter_child_nodes(node) Yield all direct child nodes of *node*, that is, all fields that are nodes and all items of fields that are lists of nodes. .. function:: walk(node) Recursively yield all descendant nodes in the tree starting at *node* (including *node* itself), in no specified order. This is useful if you only want to modify nodes in place and don't care about the context. .. class:: NodeVisitor() A node visitor base class that walks the abstract syntax tree and calls a visitor function for every node found. This function may return a value which is forwarded by the :meth:`visit` method. This class is meant to be subclassed, with the subclass adding visitor methods. .. method:: visit(node) Visit a node. The default implementation calls the method called :samp:`self.visit_{classname}` where *classname* is the name of the node class, or :meth:`generic_visit` if that method doesn't exist. .. method:: generic_visit(node) This visitor calls :meth:`visit` on all children of the node. Note that child nodes of nodes that have a custom visitor method won't be visited unless the visitor calls :meth:`generic_visit` or visits them itself. Don't use the :class:`NodeVisitor` if you want to apply changes to nodes during traversal. For this a special visitor exists (:class:`NodeTransformer`) that allows modifications. .. class:: NodeTransformer() A :class:`NodeVisitor` subclass that walks the abstract syntax tree and allows modification of nodes. The :class:`NodeTransformer` will walk the AST and use the return value of the visitor methods to replace or remove the old node. If the return value of the visitor method is ``None``, the node will be removed from its location, otherwise it is replaced with the return value. The return value may be the original node in which case no replacement takes place. Here is an example transformer that rewrites all occurrences of name lookups (``foo``) to ``data['foo']``:: class RewriteName(NodeTransformer): def visit_Name(self, node): return copy_location(Subscript( value=Name(id='data', ctx=Load()), slice=Index(value=Str(s=node.id)), ctx=node.ctx ), node) Keep in mind that if the node you're operating on has child nodes you must either transform the child nodes yourself or call the :meth:`generic_visit` method for the node first. For nodes that were part of a collection of statements (that applies to all statement nodes), the visitor may also return a list of nodes rather than just a single node. Usually you use the transformer like this:: node = YourTransformer().visit(node) .. function:: dump(node, annotate_fields=True, include_attributes=False) Return a formatted dump of the tree in *node*. This is mainly useful for debugging purposes. The returned string will show the names and the values for fields. This makes the code impossible to evaluate, so if evaluation is wanted *annotate_fields* must be set to ``False``. Attributes such as line numbers and column offsets are not dumped by default. If this is wanted, *include_attributes* can be set to ``True``.