mako/ast.py

# mako/ast.py
# Copyright 2006-2019 the Mako authors and contributors <see AUTHORS file>
#
# This module is part of Mako and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php

"""utilities for analyzing expressions and blocks of Python
code, as well as generating Python from AST nodes"""

import re

from mako import compat
from mako import exceptions
from mako import pyparser


class PythonCode(object):

    """represents information about a string containing Python code"""

    def __init__(self, code, **exception_kwargs):
        self.code = code

        # represents all identifiers which are assigned to at some point in
        # the code
        self.declared_identifiers = set()

        # represents all identifiers which are referenced before their
        # assignment, if any
        self.undeclared_identifiers = set()

        # note that an identifier can be in both the undeclared and declared
        # lists.

        # using AST to parse instead of using code.co_varnames,
        # code.co_names has several advantages:
        # - we can locate an identifier as "undeclared" even if
        # its declared later in the same block of code
        # - AST is less likely to break with version changes
        # (for example, the behavior of co_names changed a little bit
        # in python version 2.5)
        if isinstance(code, compat.string_types):
            expr = pyparser.parse(code.lstrip(), "exec", **exception_kwargs)
        else:
            expr = code

        f = pyparser.FindIdentifiers(self, **exception_kwargs)
        f.visit(expr)


class ArgumentList(object):

    """parses a fragment of code as a comma-separated list of expressions"""

    def __init__(self, code, **exception_kwargs):
        self.codeargs = []
        self.args = []
        self.declared_identifiers = set()
        self.undeclared_identifiers = set()
        if isinstance(code, compat.string_types):
            if re.match(r"\S", code) and not re.match(r",\s*$", code):
                # if theres text and no trailing comma, insure its parsed
                # as a tuple by adding a trailing comma
                code += ","
            expr = pyparser.parse(code, "exec", **exception_kwargs)
        else:
            expr = code

        f = pyparser.FindTuple(self, PythonCode, **exception_kwargs)
        f.visit(expr)


class PythonFragment(PythonCode):

    """extends PythonCode to provide identifier lookups in partial control
    statements

    e.g.::

        for x in 5:
        elif y==9:
        except (MyException, e):

    """

    def __init__(self, code, **exception_kwargs):
        m = re.match(r"^(\w+)(?:\s+(.*?))?:\s*(#|$)", code.strip(), re.S)
        if not m:
            raise exceptions.CompileException(
                "Fragment '%s' is not a partial control statement" % code,
                **exception_kwargs
            )
        if m.group(3):
            code = code[: m.start(3)]
        (keyword, expr) = m.group(1, 2)
        if keyword in ["for", "if", "while"]:
            code = code + "pass"
        elif keyword == "try":
            code = code + "pass\nexcept:pass"
        elif keyword == "elif" or keyword == "else":
            code = "if False:pass\n" + code + "pass"
        elif keyword == "except":
            code = "try:pass\n" + code + "pass"
        elif keyword == "with":
            code = code + "pass"
        else:
            raise exceptions.CompileException(
                "Unsupported control keyword: '%s'" % keyword,
                **exception_kwargs
            )
        super(PythonFragment, self).__init__(code, **exception_kwargs)


class FunctionDecl(object):

    """function declaration"""

    def __init__(self, code, allow_kwargs=True, **exception_kwargs):
        self.code = code
        expr = pyparser.parse(code, "exec", **exception_kwargs)

        f = pyparser.ParseFunc(self, **exception_kwargs)
        f.visit(expr)
        if not hasattr(self, "funcname"):
            raise exceptions.CompileException(
                "Code '%s' is not a function declaration" % code,
                **exception_kwargs
            )
        if not allow_kwargs and self.kwargs:
            raise exceptions.CompileException(
                "'**%s' keyword argument not allowed here"
                % self.kwargnames[-1],
                **exception_kwargs
            )

    def get_argument_expressions(self, as_call=False):
        """Return the argument declarations of this FunctionDecl as a printable
        list.

        By default the return value is appropriate for writing in a ``def``;
        set `as_call` to true to build arguments to be passed to the function
        instead (assuming locals with the same names as the arguments exist).
        """

        namedecls = []

        # Build in reverse order, since defaults and slurpy args come last
        argnames = self.argnames[::-1]
        kwargnames = self.kwargnames[::-1]
        defaults = self.defaults[::-1]
        kwdefaults = self.kwdefaults[::-1]

        # Named arguments
        if self.kwargs:
            namedecls.append("**" + kwargnames.pop(0))

        for name in kwargnames:
            # Keyword-only arguments must always be used by name, so even if
            # this is a call, print out `foo=foo`
            if as_call:
                namedecls.append("%s=%s" % (name, name))
            elif kwdefaults:
                default = kwdefaults.pop(0)
                if default is None:
                    # The AST always gives kwargs a default, since you can do
                    # `def foo(*, a=1, b, c=3)`
                    namedecls.append(name)
                else:
                    namedecls.append(
                        "%s=%s"
                        % (name, pyparser.ExpressionGenerator(default).value())
                    )
            else:
                namedecls.append(name)

        # Positional arguments
        if self.varargs:
            namedecls.append("*" + argnames.pop(0))

        for name in argnames:
            if as_call or not defaults:
                namedecls.append(name)
            else:
                default = defaults.pop(0)
                namedecls.append(
                    "%s=%s"
                    % (name, pyparser.ExpressionGenerator(default).value())
                )

        namedecls.reverse()
        return namedecls

    @property
    def allargnames(self):
        return tuple(self.argnames) + tuple(self.kwargnames)


class FunctionArgs(FunctionDecl):

    """the argument portion of a function declaration"""

    def __init__(self, code, **kwargs):
        super(FunctionArgs, self).__init__(
            "def ANON(%s):pass" % code, **kwargs
        )