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abc.rst.txt	11805	0644	editdlrm
aifc.rst.txt	7503	0644	editdlrm
allos.rst.txt	678	0644	editdlrm
archiving.rst.txt	440	0644	editdlrm
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ast.rst.txt	10159	0644	editdlrm
asynchat.rst.txt	8528	0644	editdlrm
asyncio-dev.rst.txt	13398	0644	editdlrm
asyncio-eventloop.rst.txt	33701	0644	editdlrm
asyncio-eventloops.rst.txt	7660	0644	editdlrm
asyncio-protocol.rst.txt	25170	0644	editdlrm
asyncio-queue.rst.txt	4328	0644	editdlrm
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asyncio.rst.txt	2272	0644	editdlrm
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atexit.rst.txt	3669	0644	editdlrm
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code.rst.txt	7817	0644	editdlrm
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collections.abc.rst.txt	12861	0644	editdlrm
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crypt.rst.txt	5122	0644	editdlrm
crypto.rst.txt	411	0644	editdlrm
csv.rst.txt	19902	0644	editdlrm
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dbm.rst.txt	14293	0644	editdlrm
debug.rst.txt	471	0644	editdlrm
decimal.rst.txt	74869	0644	editdlrm
development.rst.txt	704	0644	editdlrm
difflib.rst.txt	29861	0644	editdlrm
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distutils.rst.txt	1974	0644	editdlrm
doctest.rst.txt	71743	0644	editdlrm
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faulthandler.rst.txt	6136	0644	editdlrm
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fileinput.rst.txt	8051	0644	editdlrm
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fnmatch.rst.txt	3103	0644	editdlrm
formatter.rst.txt	13242	0644	editdlrm
fpectl.rst.txt	4180	0644	editdlrm
fractions.rst.txt	6364	0644	editdlrm
frameworks.rst.txt	391	0644	editdlrm
ftplib.rst.txt	17552	0644	editdlrm
functional.rst.txt	365	0644	editdlrm
functions.rst.txt	71621	0644	editdlrm
functools.rst.txt	18503	0644	editdlrm
gc.rst.txt	9694	0644	editdlrm
getopt.rst.txt	6557	0644	editdlrm
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grp.rst.txt	2417	0644	editdlrm
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hashlib.rst.txt	26523	0644	editdlrm
heapq.rst.txt	13402	0644	editdlrm
hmac.rst.txt	4020	0644	editdlrm
html.entities.rst.txt	1319	0644	editdlrm
html.parser.rst.txt	11275	0644	editdlrm
html.rst.txt	1304	0644	editdlrm
http.client.rst.txt	18870	0644	editdlrm
http.cookiejar.rst.txt	27832	0644	editdlrm
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http.rst.txt	7096	0644	editdlrm
http.server.rst.txt	17639	0644	editdlrm
i18n.rst.txt	408	0644	editdlrm
idle.rst.txt	25834	0644	editdlrm
imaplib.rst.txt	20367	0644	editdlrm
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imp.rst.txt	15548	0644	editdlrm
importlib.rst.txt	53563	0644	editdlrm
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ipc.rst.txt	649	0644	editdlrm
itertools.rst.txt	38459	0644	editdlrm
json.rst.txt	27876	0644	editdlrm
keyword.rst.txt	617	0644	editdlrm
language.rst.txt	522	0644	editdlrm
linecache.rst.txt	2408	0644	editdlrm
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logging.config.rst.txt	33886	0644	editdlrm
logging.handlers.rst.txt	42497	0644	editdlrm
logging.rst.txt	60479	0644	editdlrm
lzma.rst.txt	17361	0644	editdlrm
macpath.rst.txt	707	0644	editdlrm
mailbox.rst.txt	63055	0644	editdlrm
mailcap.rst.txt	3691	0644	editdlrm
markup.rst.txt	679	0644	editdlrm
marshal.rst.txt	4855	0644	editdlrm
math.rst.txt	14375	0644	editdlrm
mimetypes.rst.txt	9839	0644	editdlrm
misc.rst.txt	247	0644	editdlrm
mm.rst.txt	431	0644	editdlrm
mmap.rst.txt	11232	0644	editdlrm
modulefinder.rst.txt	3240	0644	editdlrm
modules.rst.txt	355	0644	editdlrm
msilib.rst.txt	18612	0644	editdlrm
msvcrt.rst.txt	4392	0644	editdlrm
multiprocessing.rst.txt	104494	0644	editdlrm
netdata.rst.txt	339	0644	editdlrm
netrc.rst.txt	3007	0644	editdlrm
nis.rst.txt	1993	0644	editdlrm
nntplib.rst.txt	21821	0644	editdlrm
numbers.rst.txt	8089	0644	editdlrm
numeric.rst.txt	696	0644	editdlrm
operator.rst.txt	18989	0644	editdlrm
optparse.rst.txt	76996	0644	editdlrm
os.path.rst.txt	16419	0644	editdlrm
os.rst.txt	137534	0644	editdlrm
ossaudiodev.rst.txt	17845	0644	editdlrm
othergui.rst.txt	2822	0644	editdlrm
parser.rst.txt	15148	0644	editdlrm
pathlib.rst.txt	30045	0644	editdlrm
pdb.rst.txt	19454	0644	editdlrm
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pickle.rst.txt	37440	0644	editdlrm
pickletools.rst.txt	3729	0644	editdlrm
pipes.rst.txt	2557	0644	editdlrm
pkgutil.rst.txt	8730	0644	editdlrm
platform.rst.txt	9624	0644	editdlrm
plistlib.rst.txt	7398	0644	editdlrm
poplib.rst.txt	8197	0644	editdlrm
posix.rst.txt	3694	0644	editdlrm
pprint.rst.txt	14274	0644	editdlrm
profile.rst.txt	27969	0644	editdlrm
pty.rst.txt	3123	0644	editdlrm
pwd.rst.txt	2739	0644	editdlrm
pyclbr.rst.txt	3297	0644	editdlrm
pydoc.rst.txt	4688	0644	editdlrm
pyexpat.rst.txt	28620	0644	editdlrm
python.rst.txt	475	0644	editdlrm
py_compile.rst.txt	3851	0644	editdlrm
queue.rst.txt	7268	0644	editdlrm
quopri.rst.txt	2571	0644	editdlrm
random.rst.txt	18503	0644	editdlrm
re.rst.txt	64936	0644	editdlrm
readline.rst.txt	11943	0644	editdlrm
reprlib.rst.txt	5162	0644	editdlrm
resource.rst.txt	12291	0644	editdlrm
rlcompleter.rst.txt	2294	0644	editdlrm
runpy.rst.txt	8285	0644	editdlrm
sched.rst.txt	4842	0644	editdlrm
secrets.rst.txt	5930	0644	editdlrm
select.rst.txt	28175	0644	editdlrm
selectors.rst.txt	8925	0644	editdlrm
shelve.rst.txt	8390	0644	editdlrm
shlex.rst.txt	16441	0644	editdlrm
shutil.rst.txt	26014	0644	editdlrm
signal.rst.txt	17218	0644	editdlrm
site.rst.txt	9628	0644	editdlrm
smtpd.rst.txt	10806	0644	editdlrm
smtplib.rst.txt	23439	0644	editdlrm
sndhdr.rst.txt	1994	0644	editdlrm
socket.rst.txt	68202	0644	editdlrm
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sqlite3.rst.txt	39215	0644	editdlrm
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stdtypes.rst.txt	179240	0644	editdlrm
string.rst.txt	35374	0644	editdlrm
stringprep.rst.txt	4279	0644	editdlrm
struct.rst.txt	19581	0644	editdlrm
subprocess.rst.txt	45793	0644	editdlrm
sunau.rst.txt	7390	0644	editdlrm
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symbol.rst.txt	975	0644	editdlrm
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sys.rst.txt	58273	0644	editdlrm
sysconfig.rst.txt	8749	0644	editdlrm
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tabnanny.rst.txt	2007	0644	editdlrm
tarfile.rst.txt	31749	0644	editdlrm
telnetlib.rst.txt	7899	0644	editdlrm
tempfile.rst.txt	13857	0644	editdlrm
termios.rst.txt	3751	0644	editdlrm
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xml.sax.utils.rst.txt	3901	0644	editdlrm
xmlrpc.client.rst.txt	23071	0644	editdlrm
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__future__.rst.txt	5245	0644	editdlrm
__main__.rst.txt	904	0644	editdlrm

:mod:`ast` --- Abstract Syntax Trees ==================================== .. module:: ast :synopsis: Abstract Syntax Tree classes and manipulation. .. sectionauthor:: Martin v. Löwis .. sectionauthor:: Georg Brandl **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) .. _abstract-grammar: Abstract Grammar ---------------- The abstract grammar is currently defined as follows: .. literalinclude:: ../../Parser/Python.asdl :language: none :mod:`ast` Helpers ------------------ Apart from the node classes, the :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)``. .. warning:: It is possible to crash the Python interpreter with a sufficiently large/complex string due to stack depth limitations in Python's AST compiler. .. function:: literal_eval(node_or_string) Safely evaluate an expression node or a string containing a Python literal or container display. The string or node provided may only consist of the following Python literal structures: strings, bytes, numbers, tuples, lists, dicts, sets, 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. .. warning:: It is possible to crash the Python interpreter with a sufficiently large/complex string due to stack depth limitations in Python's AST compiler. .. versionchanged:: 3.2 Now allows bytes and set literals. .. 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``. .. seealso:: `Green Tree Snakes `_, an external documentation resource, has good details on working with Python ASTs.