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Filename : fix_filter.py
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# Copyright 2007 Google, Inc. All Rights Reserved.
# Licensed to PSF under a Contributor Agreement.

"""Fixer that changes filter(F, X) into list(filter(F, X)).

We avoid the transformation if the filter() call is directly contained
in iter(<>), list(<>), tuple(<>), sorted(<>), ...join(<>), or
for V in <>:.

NOTE: This is still not correct if the original code was depending on
filter(F, X) to return a string if X is a string and a tuple if X is a
tuple.  That would require type inference, which we don't do.  Let
Python 2.6 figure it out.
"""

# Local imports
from .. import fixer_base
from ..pytree import Node
from ..pygram import python_symbols as syms
from ..fixer_util import Name, ArgList, ListComp, in_special_context, parenthesize


class FixFilter(fixer_base.ConditionalFix):
    BM_compatible = True

    PATTERN = """
    filter_lambda=power<
        'filter'
        trailer<
            '('
            arglist<
                lambdef< 'lambda'
                         (fp=NAME | vfpdef< '(' fp=NAME ')'> ) ':' xp=any
                >
                ','
                it=any
            >
            ')'
        >
        [extra_trailers=trailer*]
    >
    |
    power<
        'filter'
        trailer< '(' arglist< none='None' ',' seq=any > ')' >
        [extra_trailers=trailer*]
    >
    |
    power<
        'filter'
        args=trailer< '(' [any] ')' >
        [extra_trailers=trailer*]
    >
    """

    skip_on = "future_builtins.filter"

    def transform(self, node, results):
        if self.should_skip(node):
            return

        trailers = []
        if 'extra_trailers' in results:
            for t in results['extra_trailers']:
                trailers.append(t.clone())

        if "filter_lambda" in results:
            xp = results.get("xp").clone()
            if xp.type == syms.test:
                xp.prefix = ""
                xp = parenthesize(xp)

            new = ListComp(results.get("fp").clone(),
                           results.get("fp").clone(),
                           results.get("it").clone(), xp)
            new = Node(syms.power, [new] + trailers, prefix="")

        elif "none" in results:
            new = ListComp(Name("_f"),
                           Name("_f"),
                           results["seq"].clone(),
                           Name("_f"))
            new = Node(syms.power, [new] + trailers, prefix="")

        else:
            if in_special_context(node):
                return None

            args = results['args'].clone()
            new = Node(syms.power, [Name("filter"), args], prefix="")
            new = Node(syms.power, [Name("list"), ArgList([new])] + trailers)
            new.prefix = ""
        new.prefix = node.prefix
        return new