Python 解析与分析Python源码

>>> x = 42
>>> eval('2 + 3*4 + x')
56
>>> exec('for i in range(10): print(i)')
0
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9
>>>

>>> import ast
>>> ex = ast.parse('2 + 3*4 + x', mode='eval')
>>> ex
<_ast.Expression object at 0x1007473d0>
>>> ast.dump(ex)
"Expression(body=BinOp(left=BinOp(left=Num(n=2), op=Add(),
right=BinOp(left=Num(n=3), op=Mult(), right=Num(n=4))), op=Add(),
right=Name(id='x', ctx=Load())))"

>>> top = ast.parse('for i in range(10): print(i)', mode='exec')
>>> top
<_ast.Module object at 0x100747390>
>>> ast.dump(top)
"Module(body=[For(target=Name(id='i', ctx=Store()),
iter=Call(func=Name(id='range', ctx=Load()), args=[Num(n=10)],
keywords=[], starargs=None, kwargs=None),
body=[Expr(value=Call(func=Name(id='print', ctx=Load()),
args=[Name(id='i', ctx=Load())], keywords=[], starargs=None,
kwargs=None))], orelse=[])])"
>>>

import ast

class CodeAnalyzer(ast.NodeVisitor):
    def __init__(self):
        self.loaded = set()
        self.stored = set()
        self.deleted = set()

    def visit_Name(self, node):
        if isinstance(node.ctx, ast.Load):
            self.loaded.add(node.id)
        elif isinstance(node.ctx, ast.Store):
            self.stored.add(node.id)
        elif isinstance(node.ctx, ast.Del):
            self.deleted.add(node.id)

# Sample usage
if __name__ == '__main__':
    # Some Python code
    code = '''
    for i in range(10):
        print(i)
    del i
    '''

    # Parse into an AST
    top = ast.parse(code, mode='exec')

    # Feed the AST to analyze name usage
    c = CodeAnalyzer()
    c.visit(top)
    print('Loaded:', c.loaded)
    print('Stored:', c.stored)
    print('Deleted:', c.deleted)

Loaded: {'i', 'range', 'print'}
Stored: {'i'}
Deleted: {'i'}

>>> exec(compile(top,'<stdin>', 'exec'))
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>>>

# namelower.py
import ast
import inspect

# Node visitor that lowers globally accessed names into
# the function body as local variables.
class NameLower(ast.NodeVisitor):
    def __init__(self, lowered_names):
        self.lowered_names = lowered_names

    def visit_FunctionDef(self, node):
        # Compile some assignments to lower the constants
        code = '__globals = globals()\n'
        code += '\n'.join("{0} = __globals['{0}']".format(name)
                            for name in self.lowered_names)
        code_ast = ast.parse(code, mode='exec')

        # Inject new statements into the function body
        node.body[:0] = code_ast.body

        # Save the function object
        self.func = node

# Decorator that turns global names into locals
def lower_names(*namelist):
    def lower(func):
        srclines = inspect.getsource(func).splitlines()
        # Skip source lines prior to the @lower_names decorator
        for n, line in enumerate(srclines):
            if '@lower_names' in line:
                break

        src = '\n'.join(srclines[n+1:])
        # Hack to deal with indented code
        if src.startswith((' ','\t')):
            src = 'if 1:\n' + src
        top = ast.parse(src, mode='exec')

        # Transform the AST
        cl = NameLower(namelist)
        cl.visit(top)

        # Execute the modified AST
        temp = {}
        exec(compile(top,'','exec'), temp, temp)

        # Pull out the modified code object
        func.__code__ = temp[func.__name__].__code__
        return func
    return lower

INCR = 1
@lower_names('INCR')
def countdown(n):
    while n > 0:
        n -= INCR

def countdown(n):
    __globals = globals()
    INCR = __globals['INCR']
    while n > 0:
        n -= INCR