/Lib/lib2to3/fixes/fix_tuple_params.py

  1"""Fixer for function definitions with tuple parameters.
  2
  3def func(((a, b), c), d):
  4    ...
  5
  6    ->
  7
  8def func(x, d):
  9    ((a, b), c) = x
 10    ...
 11
 12It will also support lambdas:
 13
 14    lambda (x, y): x + y -> lambda t: t[0] + t[1]
 15
 16    # The parens are a syntax error in Python 3
 17    lambda (x): x + y -> lambda x: x + y
 18"""
 19# Author: Collin Winter
 20
 21# Local imports
 22from .. import pytree
 23from ..pgen2 import token
 24from .. import fixer_base
 25from ..fixer_util import Assign, Name, Newline, Number, Subscript, syms
 26
 27def is_docstring(stmt):
 28    return isinstance(stmt, pytree.Node) and \
 29           stmt.children[0].type == token.STRING
 30
 31class FixTupleParams(fixer_base.BaseFix):
 32    PATTERN = """
 33              funcdef< 'def' any parameters< '(' args=any ')' >
 34                       ['->' any] ':' suite=any+ >
 35              |
 36              lambda=
 37              lambdef< 'lambda' args=vfpdef< '(' inner=any ')' >
 38                       ':' body=any
 39              >
 40              """
 41
 42    def transform(self, node, results):
 43        if "lambda" in results:
 44            return self.transform_lambda(node, results)
 45
 46        new_lines = []
 47        suite = results["suite"]
 48        args = results["args"]
 49        # This crap is so "def foo(...): x = 5; y = 7" is handled correctly.
 50        # TODO(cwinter): suite-cleanup
 51        if suite[0].children[1].type == token.INDENT:
 52            start = 2
 53            indent = suite[0].children[1].value
 54            end = Newline()
 55        else:
 56            start = 0
 57            indent = "; "
 58            end = pytree.Leaf(token.INDENT, "")
 59
 60        # We need access to self for new_name(), and making this a method
 61        #  doesn't feel right. Closing over self and new_lines makes the
 62        #  code below cleaner.
 63        def handle_tuple(tuple_arg, add_prefix=False):
 64            n = Name(self.new_name())
 65            arg = tuple_arg.clone()
 66            arg.set_prefix("")
 67            stmt = Assign(arg, n.clone())
 68            if add_prefix:
 69                n.set_prefix(" ")
 70            tuple_arg.replace(n)
 71            new_lines.append(pytree.Node(syms.simple_stmt,
 72                                         [stmt, end.clone()]))
 73
 74        if args.type == syms.tfpdef:
 75            handle_tuple(args)
 76        elif args.type == syms.typedargslist:
 77            for i, arg in enumerate(args.children):
 78                if arg.type == syms.tfpdef:
 79                    # Without add_prefix, the emitted code is correct,
 80                    #  just ugly.
 81                    handle_tuple(arg, add_prefix=(i > 0))
 82
 83        if not new_lines:
 84            return node
 85
 86        # This isn't strictly necessary, but it plays nicely with other fixers.
 87        # TODO(cwinter) get rid of this when children becomes a smart list
 88        for line in new_lines:
 89            line.parent = suite[0]
 90
 91        # TODO(cwinter) suite-cleanup
 92        after = start
 93        if start == 0:
 94            new_lines[0].set_prefix(" ")
 95        elif is_docstring(suite[0].children[start]):
 96            new_lines[0].set_prefix(indent)
 97            after = start + 1
 98
 99        suite[0].children[after:after] = new_lines
100        for i in range(after+1, after+len(new_lines)+1):
101            suite[0].children[i].set_prefix(indent)
102        suite[0].changed()
103
104    def transform_lambda(self, node, results):
105        args = results["args"]
106        body = results["body"]
107        inner = simplify_args(results["inner"])
108
109        # Replace lambda ((((x)))): x  with lambda x: x
110        if inner.type == token.NAME:
111            inner = inner.clone()
112            inner.set_prefix(" ")
113            args.replace(inner)
114            return
115
116        params = find_params(args)
117        to_index = map_to_index(params)
118        tup_name = self.new_name(tuple_name(params))
119
120        new_param = Name(tup_name, prefix=" ")
121        args.replace(new_param.clone())
122        for n in body.post_order():
123            if n.type == token.NAME and n.value in to_index:
124                subscripts = [c.clone() for c in to_index[n.value]]
125                new = pytree.Node(syms.power,
126                                  [new_param.clone()] + subscripts)
127                new.set_prefix(n.get_prefix())
128                n.replace(new)
129
130
131### Helper functions for transform_lambda()
132
133def simplify_args(node):
134    if node.type in (syms.vfplist, token.NAME):
135        return node
136    elif node.type == syms.vfpdef:
137        # These look like vfpdef< '(' x ')' > where x is NAME
138        # or another vfpdef instance (leading to recursion).
139        while node.type == syms.vfpdef:
140            node = node.children[1]
141        return node
142    raise RuntimeError("Received unexpected node %s" % node)
143
144def find_params(node):
145    if node.type == syms.vfpdef:
146        return find_params(node.children[1])
147    elif node.type == token.NAME:
148        return node.value
149    return [find_params(c) for c in node.children if c.type != token.COMMA]
150
151def map_to_index(param_list, prefix=[], d=None):
152    if d is None:
153        d = {}
154    for i, obj in enumerate(param_list):
155        trailer = [Subscript(Number(i))]
156        if isinstance(obj, list):
157            map_to_index(obj, trailer, d=d)
158        else:
159            d[obj] = prefix + trailer
160    return d
161
162def tuple_name(param_list):
163    l = []
164    for obj in param_list:
165        if isinstance(obj, list):
166            l.append(tuple_name(obj))
167        else:
168            l.append(obj)
169    return "_".join(l)