Preview: fix_except.py
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/opt/alt/python37/lib64/python3.7/lib2to3/fixes/fix_except.py
"""Fixer for except statements with named exceptions.
The following cases will be converted:
- "except E, T:" where T is a name:
except E as T:
- "except E, T:" where T is not a name, tuple or list:
except E as t:
T = t
This is done because the target of an "except" clause must be a
name.
- "except E, T:" where T is a tuple or list literal:
except E as t:
T = t.args
"""
# Author: Collin Winter
# Local imports
from .. import pytree
from ..pgen2 import token
from .. import fixer_base
from ..fixer_util import Assign, Attr, Name, is_tuple, is_list, syms
def find_excepts(nodes):
for i, n in enumerate(nodes):
if n.type == syms.except_clause:
if n.children[0].value == 'except':
yield (n, nodes[i+2])
class FixExcept(fixer_base.BaseFix):
BM_compatible = True
PATTERN = """
try_stmt< 'try' ':' (simple_stmt | suite)
cleanup=(except_clause ':' (simple_stmt | suite))+
tail=(['except' ':' (simple_stmt | suite)]
['else' ':' (simple_stmt | suite)]
['finally' ':' (simple_stmt | suite)]) >
"""
def transform(self, node, results):
syms = self.syms
tail = [n.clone() for n in results["tail"]]
try_cleanup = [ch.clone() for ch in results["cleanup"]]
for except_clause, e_suite in find_excepts(try_cleanup):
if len(except_clause.children) == 4:
(E, comma, N) = except_clause.children[1:4]
comma.replace(Name("as", prefix=" "))
if N.type != token.NAME:
# Generate a new N for the except clause
new_N = Name(self.new_name(), prefix=" ")
target = N.clone()
target.prefix = ""
N.replace(new_N)
new_N = new_N.clone()
# Insert "old_N = new_N" as the first statement in
# the except body. This loop skips leading whitespace
# and indents
#TODO(cwinter) suite-cleanup
suite_stmts = e_suite.children
for i, stmt in enumerate(suite_stmts):
if isinstance(stmt, pytree.Node):
break
# The assignment is different if old_N is a tuple or list
# In that case, the assignment is old_N = new_N.args
if is_tuple(N) or is_list(N):
assign = Assign(target, Attr(new_N, Name('args')))
else:
assign = Assign(target, new_N)
#TODO(cwinter) stopgap until children becomes a smart list
for child in reversed(suite_stmts[:i]):
e_suite.insert_child(0, child)
e_suite.insert_child(i, assign)
elif N.prefix == "":
# No space after a comma is legal; no space after "as",
# not so much.
N.prefix = " "
#TODO(cwinter) fix this when children becomes a smart list
children = [c.clone() for c in node.children[:3]] + try_cleanup + tail
return pytree.Node(node.type, children)
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