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如何获取Python对象的源代码

有时候我们会想要知道某个Python函数、类或者模块(我们把这些东西统称为Python的对象)是怎么定义的,或者找出它们是在哪个文件中定义的。

有两个库能够帮我们做到这一点,一个是内置的 inspect 库,一个是第三方的 dill

inspect库

help(inspect) 能看到关于 inspect 的描述如下:

DESCRIPTION
    This module encapsulates the interface provided by the internal special
    attributes (co_*, im_*, tb_*, etc.) in a friendlier fashion.
    It also provides some help for examining source code and class layout.

我们主要是使用该模块的 getsource* 系列函数,即:

  1. inspect.getsource(object) 函数以单字符串的形式返回某个python对象的源代码

    import inspect
    return inspect.getsource(inspect.getsource)
    
    def getsource(object):
        """Return the text of the source code for an object.
    
        The argument may be a module, class, method, function, traceback, frame,
        or code object.  The source code is returned as a single string.  An
        OSError is raised if the source code cannot be retrieved."""
        lines, lnum = getsourcelines(object)
        return ''.join(lines)
    
  2. inspect.getsourcefile(object) 函数返回某个python对象在哪个文件中定义

    import inspect
    return inspect.getsourcefile(inspect.getsourcefile)
    
    /usr/lib/python3.6/inspect.py
    
  3. inspect.getsourcelines(object) 函数返回一个元组,其中包含了python对象源代码的list,以及其在源代码中定义的起始行

    import inspect
    return inspect.getsourcelines(inspect.getsourcelines)
    
    (['def getsourcelines(object):\n', '    """Return a list of source lines and starting line number for an object.\n', '\n', '    The argument may be a module, class, method, function, traceback, frame,\n', '    or code object.  The source code is returned as a list of the lines\n', '    corresponding to the object and the line number indicates where in the\n', '    original source file the first line of code was found.  An OSError is\n', '    raised if the source code cannot be retrieved."""\n', '    object = unwrap(object)\n', '    lines, lnum = findsource(object)\n', '\n', '    if ismodule(object):\n', '        return lines, 0\n', '    else:\n', '        return getblock(lines[lnum:]), lnum + 1\n'], 946)
    

然而, inspect 有一个缺陷,那就是无法获取interactive python session中定义对象的源代码:

import inspect
def sum(a,b):
    return a+b
return inspect.getsource(sum)
Traceback (most recent call last):
  File "<stdin>", line 8, in <module>
  File "<stdin>", line 6, in main
  File "/usr/lib/python3.6/inspect.py", line 968, in getsource
    lines, lnum = getsourcelines(object)
  File "/usr/lib/python3.6/inspect.py", line 955, in getsourcelines
    lines, lnum = findsource(object)
  File "/usr/lib/python3.6/inspect.py", line 786, in findsource
    raise OSError('could not get source code')
OSError: could not get source code

若想要能够获取interactive python session中定义对象的源代码,则可以使用第三方的 dill

dill库

dill 有一个 source 子module,它提供了跟 inspect 非常类似的API接口:

  1. dill.source.getsource函数

    import dill
    return dill.source.getsource(dill.source.getsource)
    
    def getsource(object, alias='', lstrip=False, enclosing=False, \
                                                  force=False, builtin=False):
        """Return the text of the source code for an object. The source code for
        interactively-defined objects are extracted from the interpreter's history.
    
        The argument may be a module, class, method, function, traceback, frame,
        or code object.  The source code is returned as a single string.  An
        IOError is raised if the source code cannot be retrieved, while a
        TypeError is raised for objects where the source code is unavailable
        (e.g. builtins).
    
        If alias is provided, then add a line of code that renames the object.
        If lstrip=True, ensure there is no indentation in the first line of code.
        If enclosing=True, then also return any enclosing code.
        If force=True, catch (TypeError,IOError) and try to use import hooks.
        If builtin=True, force an import for any builtins
        """
        # hascode denotes a callable
        hascode = _hascode(object)
        # is a class instance type (and not in builtins)
        instance = _isinstance(object)
    
        # get source lines; if fail, try to 'force' an import
        try: # fails for builtins, and other assorted object types
            lines, lnum = getsourcelines(object, enclosing=enclosing)
        except (TypeError, IOError): # failed to get source, resort to import hooks
            if not force: # don't try to get types that findsource can't get
                raise
            if not getmodule(object): # get things like 'None' and '1'
                if not instance: return getimport(object, alias, builtin=builtin)
                # special handling (numpy arrays, ...)
                _import = getimport(object, builtin=builtin)
                name = getname(object, force=True)
                _alias = "%s = " % alias if alias else ""
                if alias == name: _alias = ""
                return _import+_alias+"%s\n" % name
            else: #FIXME: could use a good bit of cleanup, since using getimport...
                if not instance: return getimport(object, alias, builtin=builtin)
                # now we are dealing with an instance...
                name = object.__class__.__name__
                module = object.__module__
                if module in ['builtins','__builtin__']:
                    return getimport(object, alias, builtin=builtin)
                else: #FIXME: leverage getimport? use 'from module import name'?
                    lines, lnum = ["%s = __import__('%s', fromlist=['%s']).%s\n" % (name,module,name,name)], 0
                    obj = eval(lines[0].lstrip(name + ' = '))
                    lines, lnum = getsourcelines(obj, enclosing=enclosing)
    
        # strip leading indent (helps ensure can be imported)
        if lstrip or alias:
            lines = _outdent(lines)
    
        # instantiate, if there's a nice repr  #XXX: BAD IDEA???
        if instance: #and force: #XXX: move into findsource or getsourcelines ?
            if '(' in repr(object): lines.append('%r\n' % object)
           #else: #XXX: better to somehow to leverage __reduce__ ?
           #    reconstructor,args = object.__reduce__()
           #    _ = reconstructor(*args)
            else: # fall back to serialization #XXX: bad idea?
                #XXX: better not duplicate work? #XXX: better new/enclose=True?
                lines = dumpsource(object, alias='', new=force, enclose=False)
                lines, lnum = [line+'\n' for line in lines.split('\n')][:-1], 0
           #else: object.__code__ # raise AttributeError
    
        # add an alias to the source code
        if alias:
            if hascode:
                skip = 0
                for line in lines: # skip lines that are decorators
                    if not line.startswith('@'): break
                    skip += 1
                #XXX: use regex from findsource / getsourcelines ?
                if lines[skip].lstrip().startswith('def '): # we have a function
                    if alias != object.__name__:
                        lines.append('\n%s = %s\n' % (alias, object.__name__))
                elif 'lambda ' in lines[skip]: # we have a lambda
                    if alias != lines[skip].split('=')[0].strip():
                        lines[skip] = '%s = %s' % (alias, lines[skip])
                else: # ...try to use the object's name
                    if alias != object.__name__:
                        lines.append('\n%s = %s\n' % (alias, object.__name__))
            else: # class or class instance
                if instance:
                    if alias != lines[-1].split('=')[0].strip():
                        lines[-1] = ('%s = ' % alias) + lines[-1]
                else:
                    name = getname(object, force=True) or object.__name__
                    if alias != name:
                        lines.append('\n%s = %s\n' % (alias, name))
        return ''.join(lines)
    
  2. dill.source.getsourcefile函数

    import dill
    return dill.source.getsourcefile(dill.source.getsourcefile)
    
    /usr/lib/python3.6/inspect.py
    
  3. dill.source.getsourcelines函数

    import dill
    return dill.source.getsourcelines(dill.source.getsourcelines)
    
    (['def getsourcelines(object, lstrip=False, enclosing=False):\n', '    """Return a list of source lines and starting line number for an object.\n', "    Interactively-defined objects refer to lines in the interpreter's history.\n", '\n', '    The argument may be a module, class, method, function, traceback, frame,\n', '    or code object.  The source code is returned as a list of the lines\n', '    corresponding to the object and the line number indicates where in the\n', '    original source file the first line of code was found.  An IOError is\n', '    raised if the source code cannot be retrieved, while a TypeError is\n', '    raised for objects where the source code is unavailable (e.g. builtins).\n', '\n', '    If lstrip=True, ensure there is no indentation in the first line of code.\n', '    If enclosing=True, then also return any enclosing code."""\n', '    code, n = getblocks(object, lstrip=lstrip, enclosing=enclosing, locate=True)\n', '    return code[-1], n[-1]\n'], 300)
    

不过它还支持获取interactive python session中定义对象的源代码: screenshot-01.png