435 lines
13 KiB
Python
435 lines
13 KiB
Python
'''
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Find code patterns that PEP-505 attempts to make more concise.
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Example usage:
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$ find /usr/lib/python3.4 -name '*.py' | xargs python3 find-pep505.py
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'''
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import ast
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import sys
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class NoneCoalesceIfBlockVisitor(ast.NodeVisitor):
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'''
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Look for if blocks of the form:
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>>> if a is None:
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... a = b
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>>> if a is not None:
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... b
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... else:
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... a = c
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>>> def foo(self, a=None):
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... if a is None:
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... self.b = c
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... else:
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... self.b = a
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>>> def foo(self, a=None):
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... if a is not None:
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... self.b = a
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... else:
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... self.b = c
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...where `a` is a name and other characters represent any abitrary
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expression.
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In the two latter forms, the search criterion is an assignment of `a`
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to any identifier in the `a is not None` block.
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'''
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def __init__(self, file_, callback):
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self.__file = file_
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self.__callback = callback
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def visit_If(self, if_):
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if not isinstance(if_.test, ast.Compare):
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return
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op = if_.test.ops[0]
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# Match `if a is None:` or `if a is not None:`, where `a` is a name.
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if isinstance(op, (ast.Is, ast.IsNot)) and \
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isinstance(if_.test.left, ast.Name) and \
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isinstance(if_.test.comparators[0], ast.NameConstant) and \
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if_.test.comparators[0].value is None:
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test_name = if_.test.left.id
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else:
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return
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# Keep track of which block handles the `a is None` condition and which
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# handles the `a is not None` condition.
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if isinstance(op, ast.Is):
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none_block = if_.body
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value_block = if_.orelse
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elif isinstance(op, ast.IsNot):
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none_block = if_.orelse
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value_block = if_.body
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if len(none_block) != 1:
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return
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none_stmt = none_block[0]
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# If there is no `a is not None` block, handle gracefully.
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if len(value_block) == 1:
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value_stmt = value_block[0]
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else:
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value_stmt = None
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# Assigning a value to `a` when it is `None`?
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if isinstance(none_stmt, ast.Assign) and \
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len(none_stmt.targets) == 1:
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target = none_stmt.targets[0]
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if isinstance(target, ast.Name):
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if test_name == target.id:
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self.__callback(self.__file, if_.test.lineno,
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target.lineno)
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return
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# Assigning value of `a` to another identifier when a is not `None`?
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if isinstance(value_stmt, ast.Assign) and \
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isinstance(value_stmt.value, ast.Name) and \
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test_name == value_stmt.value.id:
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end_line = max(value_stmt.lineno, none_stmt.lineno)
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self.__callback(self.__file, if_.test.lineno, end_line)
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class NoneCoalesceOrVisitor(ast.NodeVisitor):
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'''
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Look for expressions of the form:
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>>> a or '1'
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>>> a or []
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>>> a or {}
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...where `a` is any name. More formally, match a plain name on the left side
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of `or` and something that looks like a default on the right, e.g. a
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constant or a constructor invocation.
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'''
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def __init__(self, file_, callback):
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self.__file = file_
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self.__callback = callback
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def visit_BoolOp(self, bool_op):
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if not isinstance(bool_op.op, ast.Or) or \
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not isinstance(bool_op.values[0], ast.Name):
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return
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defaults = ast.Call, ast.Dict, ast.List, ast.Num, ast.Set, ast.Str
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if isinstance(bool_op.values[1], defaults):
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start_line = bool_op.values[0].lineno
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end_line = bool_op.values[-1].lineno
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self.__callback(self.__file, start_line, end_line)
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class NoneCoalesceTernaryVisitor(ast.NodeVisitor):
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'''
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Look for ternary expressions of the form:
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>>> a if a is not None else b
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>>> b if a is None else a
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...where a is an identifier and b is an abitrary expression.
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'''
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def __init__(self, file_, callback):
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self.__file = file_
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self.__callback = callback
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def visit_IfExp(self, ifexp):
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if isinstance(ifexp.test, ast.Compare):
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op = ifexp.test.ops[0]
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# Match `a is None` or `a is not None`, where `a` is a name.
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if isinstance(op, (ast.Is, ast.IsNot)) and \
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isinstance(ifexp.test.left, ast.Name) and \
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isinstance(ifexp.test.comparators[0], ast.NameConstant) and \
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ifexp.test.comparators[0].value is None:
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test_name = ifexp.test.left.id
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else:
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return
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if isinstance(op, ast.IsNot) and isinstance(ifexp.body, ast.Name):
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# Match `a if a is not None else ...`.
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result_name = ifexp.body.id
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elif isinstance(op, ast.Is) and isinstance(ifexp.orelse, ast.Name):
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# Match `... if a is None else a`.
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result_name = ifexp.orelse.id
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else:
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return
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if test_name == result_name:
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self.__callback(self.__file, ifexp.test.lineno, None)
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class SafeNavAndVisitor(ast.NodeVisitor):
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'''
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Look for expressions where `and` is used to avoid attribute/index access on
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``None``:
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>>> a and a.foo
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>>> a and a[foo]
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>>> a and a.foo()
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>>> a and a.foo.bar
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...where `a` is any name and `foo`, `bar` are any attribute or keys.
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'''
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def __init__(self, file_, callback):
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self.__file = file_
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self.__callback = callback
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def visit_BoolOp(self, bool_op):
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if not isinstance(bool_op.op, ast.And) or \
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not isinstance(bool_op.values[0], ast.Name):
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return
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left_name = bool_op.values[0].id
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right = bool_op.values[1]
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if isinstance(right, (ast.Attribute, ast.Call, ast.Subscript)):
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right_name = get_name_from_node(right)
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else:
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return
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if left_name == right_name:
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start_line = bool_op.values[0].lineno
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end_line = bool_op.values[-1].lineno
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self.__callback(self.__file, start_line, end_line)
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class SafeNavIfBlockVisitor(ast.NodeVisitor):
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'''
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Look for blocks where `if` is used to avoid attribute/index access on
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``None``:
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>>> if a is not None:
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... a.foo
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>>> if a is None:
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... pass
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... else:
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... a.foo
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...where `a` is any name. Index access and function calls are also matched.
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'''
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def __init__(self, file_, callback):
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self.__file = file_
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self.__callback = callback
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def visit_If(self, if_):
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if not isinstance(if_.test, ast.Compare):
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return
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op = if_.test.ops[0]
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# Match `if a is None:` or `if a is not None:`, where `a` is a name.
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if isinstance(op, (ast.Is, ast.IsNot)) and \
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isinstance(if_.test.left, ast.Name) and \
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isinstance(if_.test.comparators[0], ast.NameConstant) and \
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if_.test.comparators[0].value is None:
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test_name = if_.test.left.id
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else:
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return
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# Keep track of which block handles the `a is None` condition and which
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# handles the `a is not None` condition.
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if isinstance(op, ast.Is):
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none_block = if_.body
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value_block = if_.orelse
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elif isinstance(op, ast.IsNot):
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none_block = if_.orelse
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value_block = if_.body
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if len(none_block) > 0:
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none_lineno = none_block[0].lineno
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else:
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none_lineno = 0
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# If there is no `a is not None` block, then it's definitely not a
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# match.
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if len(value_block) == 1:
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value_stmt = value_block[0]
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else:
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return
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# Assigning the value of `a.foo` or `a[foo]` or calling `a.foo()` in the
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# `a is not None` block. (But don't match bare `a` -- that's already
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# covered by the None coalesce visitors.)
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if isinstance(value_stmt, (ast.Assign, ast.Expr)) and \
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not isinstance(value_stmt.value, ast.Name):
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expr_name = get_name_from_node(value_stmt.value)
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else:
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return
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# Assigning value of `a` to another identifier when a is not `None`?
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if test_name == expr_name:
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end_line = max(value_stmt.lineno, none_lineno)
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self.__callback(self.__file, if_.test.lineno, end_line)
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class SafeNavTernaryVisitor(ast.NodeVisitor):
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'''
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Look for ternary expressions of the form:
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>>> a.foo if a is not None else b
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>>> b if a is None else a.foo
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...where `a` is an identifier, `b` is an abitrary expression, and `foo` is
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an attribute, index, or function invocation.
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'''
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def __init__(self, file_, callback):
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self.__file = file_
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self.__callback = callback
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def visit_IfExp(self, ifexp):
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if isinstance(ifexp.test, ast.Compare):
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op = ifexp.test.ops[0]
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# Match `a is None` or `a is not None`, where `a` is a name.
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if isinstance(op, (ast.Is, ast.IsNot)) and \
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isinstance(ifexp.test.left, ast.Name) and \
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isinstance(ifexp.test.comparators[0], ast.NameConstant) and \
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ifexp.test.comparators[0].value is None:
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test_name = ifexp.test.left.id
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else:
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return
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exprs = ast.Attribute, ast.Call, ast.Subscript
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if isinstance(op, ast.IsNot) and isinstance(ifexp.body, exprs):
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# Match `a.foo if a is not None else ...`.
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result_name = get_name_from_node(ifexp.body)
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elif isinstance(op, ast.Is) and isinstance(ifexp.orelse, exprs):
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# Match `... if a is None else a.foo`.
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result_name = get_name_from_node(ifexp.orelse)
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else:
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return
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if test_name == result_name:
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self.__callback(self.__file, ifexp.test.lineno, None)
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def count_calls_decorator(callback):
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'''
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Decorator for a callback that counts how many time that callback
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was invoked.
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'''
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def invoke(*args):
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callback(*args)
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invoke.count += 1
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invoke.count = 0
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return invoke
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def get_call_count(invoke):
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'''
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In tandem with `count_calls_decorator`, return the number of times that
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a callback was invoked.
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'''
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return invoke.count
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def get_name_from_node(node):
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'''
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Return the left-most name from an Attribute or Subscript node.
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'''
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while isinstance(node, (ast.Attribute, ast.Call, ast.Subscript)):
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if isinstance(node, ast.Call):
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node = node.func
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else:
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node = node.value
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if isinstance(node, ast.Name):
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return node.id
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else:
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return None
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def log(text, file_, start_line, stop_line=None):
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'''
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Display a match, including file name, line number, and code excerpt.
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'''
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print('{}: {}:{}'.format(text, file_, start_line))
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if stop_line is None:
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stop_line = start_line
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with open(file_) as source:
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print(''.join(source.readlines()[start_line-1:stop_line]))
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def main():
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if len(sys.argv) < 2:
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sys.stderr.write('Usage: python3 parse.py <files>\n')
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sys.exit(1)
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def make_callback(text):
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return count_calls_decorator(
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lambda file_, start, stop: log(text, file_, start, stop)
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)
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nci_callback = make_callback('None-coalescing `if` block')
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nco_callback = make_callback('[Possible] None-coalescing `or`')
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nct_callback = make_callback('None-coalescing ternary')
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sna_callback = make_callback('Safe navigation `and`')
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sni_callback = make_callback('Safe navigation `if` block')
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snt_callback = make_callback('Safe navigation ternary')
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for file_ in sys.argv[1:]:
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with open(file_) as source:
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tree = ast.parse(source.read(), filename=file_)
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NoneCoalesceIfBlockVisitor(file_, nci_callback).visit(tree)
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NoneCoalesceOrVisitor(file_, nco_callback).visit(tree)
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NoneCoalesceTernaryVisitor(file_, nct_callback).visit(tree)
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SafeNavAndVisitor(file_, sna_callback).visit(tree)
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SafeNavIfBlockVisitor(file_, sni_callback).visit(tree)
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SafeNavTernaryVisitor(file_, snt_callback).visit(tree)
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print('Total None-coalescing `if` blocks: {}'
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.format(get_call_count(nci_callback)))
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print('Total [possible] None-coalescing `or`: {}'
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.format(get_call_count(nco_callback)))
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print('Total None-coalescing ternaries: {}'
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.format(get_call_count(nct_callback)))
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print('Total Safe navigation `and`: {}'
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.format(get_call_count(sna_callback)))
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print('Total Safe navigation `if` blocks: {}'
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.format(get_call_count(sni_callback)))
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print('Total Safe navigation ternaries: {}'
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.format(get_call_count(snt_callback)))
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if __name__ == '__main__':
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main()
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