from pychecker2.Check import Check
from pychecker2.util import BaseVisitor
from pychecker2.Warning import Warning
from compiler import ast,walk
class ReachableCheck(Check):
unreachable = Warning('Report unreachable code', 'Line is unreachable')
implicitReturn = \
Warning('Report implicit return in a function with explicit returns',
'Function %s uses both implicit and explicit returns')
def check(self, file, unused_checker):
class ReturnsVisitor(BaseVisitor):
def __init__(s):
s.always_returns = 0 # icky: result value by side-effect
s.has_returns = 0
def check_returns(s, node):
s.always_returns = 0
s.visit(node)
return s.always_returns
def alternatives_with_else(s, nodes, else_):
for n in nodes:
if not s.check_returns(n):
return
s.always_returns = 0
if else_:
s.visit(else_)
def visitAssert(s, node):
if isinstance(node.test, ast.Const):
s.always_returns = not node.test.value
if isinstance(node.test, ast.Name):
if node.test.name == 'None':
s.always_returns = 1
def visitReturn(s, node):
s.always_returns = 1
if not isinstance(node.value, ast.Const) or \
node.value.value is not None:
s.has_returns = 1
def visitRaise(s, unused_node):
s.always_returns = 1
def visitTryExcept(s, node):
# if body always returns, else code is unreachable
if s.check_returns(node.body) and node.else_:
file.warning(node.else_.nodes[0], self.unreachable)
s.always_returns = 0
# no matter what happens in the try clause, it might
# cause an exception, so check the handlers and else
# conditions all return
handlers = [code for exc, detail, code in node.handlers]
s.alternatives_with_else(handlers, node.else_ or node.body)
def visitIf(s, node):
code = [code for cond, code in node.tests]
s.alternatives_with_else(code, node.else_)
def visitStmt(s, node):
for n in range(len(node.nodes) - 1):
if s.check_returns(node.nodes[n]):
file.warning(node.nodes[n + 1], self.unreachable)
break
else:
if node.nodes and \
not s.check_returns(node.nodes[-1]) and \
isinstance(node.parent, ast.Function) and \
s.has_returns:
file.warning(node.nodes[-1], self.implicitReturn,
node.parent.name)
def visitFunction(s, node):
pass
visitClass = visitFunction
def visitWhile(s, unused):
# FIXME: while's may never execute and not return
s.always_returns = 0
visitFor = visitWhile
for scope in file.scopes.values():
if isinstance(scope.node, ast.Function):
walk(scope.node.code, ReturnsVisitor())
|