獲取Python函式資訊的方法

Python的反射機制可以動態獲取物件資訊以及動態呼叫物件，本文介紹如何獲取物件中的函式注釋資訊以及引數資訊，

定義一個Person類：

class Person():
    def talk(self, name, age, height=None):
        """talk function
        :return:
        """
        print(f"My name is {name}")
        print(f"My age is {age}")
        if height is not None:
            print(f"My height is {height}")

dir() 命令也可以獲取函式的屬性資訊：

person = Person()
print(dir(person))

func = getattr(person, "talk")
print(dir(func))

結果

['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'talk']

['__call__', '__class__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__func__', '__ge__', '__get__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__self__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__']

獲取函式注釋資訊

可以通過 doc 屬性來獲取注釋資訊（三引號括起來的注釋）：

func = getattr(person, "talk")
print(func.__doc__)

結果

talk function
        :return:

獲取函式引數

1、 通過 __code__ 屬性讀取函式引數資訊

>> print(dir(func.__code__))
['__class__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'co_argcount', 'co_cellvars', 'co_code', 'co_consts', 'co_filename', 'co_firstlineno', 'co_flags', 'co_freevars', 'co_kwonlyargcount', 'co_lnotab', 'co_name', 'co_names', 'co_nlocals', 'co_stacksize', 'co_varnames']>>

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print("co_name: ", func.__code__.co_name)  # 回傳函式名
print("co_argcount: ", func.__code__.co_argcount)  # 回傳函式的引數個數
print("co_varnames: ",func.__code__.co_varnames) # 回傳函式的引數
print("co_filename: ", func.__code__.co_filename) # 回傳檔案絕對路徑
print("co_consts: ", func.__code__.co_consts)
print("co_firstlineno: ",func.__code__.co_firstlineno) # 回傳函式行號
print("co_kwonlyargcount: ",func.__code__.co_kwonlyargcount) # 關鍵字引數
print("co_nlocals: ",func.__code__.co_nlocals) # 回傳區域變數個數

結果

co_name:  talk
co_argcount:  4
co_varnames:  ('self', 'name', 'age', 'height')
co_filename:  D:/ProgramWorkspace/PythonNotes/00-Python-Essentials/demo.py
co_consts:  ('talk function\n        :return:\n        ', 'My name is ', 'My age is ', None, 'My height is ')
co_firstlineno:  44
co_kwonlyargcount:  0
co_nlocals:  4

通過 code.co_varnames 可以獲取引數名，引數默認值可以通過如下方式獲得：

print(func.__defaults__)

結果

(None,)

2、通過inspect庫來讀取函式引數資訊

除了用__code__ 屬性外還可以使用inspect庫來讀取函式引數，使用getfullargspec和signature方法來讀取函式引數：

import inspect

# inspect.getargspec(func) # python2
argspec = inspect.getfullargspec(func)
print(argspec.args)
print(argspec.defaults)
print(argspec.varkw)
sig = inspect.signature(func)
print(sig)

結果

['self', 'name', 'age', 'height']
(None,)
None
(name, age, height=None)

也可以在函式內部使用：

class Person():
    def talk(self, name, age, height=None):
        """talk function
        :return:
        """
        frame = inspect.currentframe()
        args, _, _, values = inspect.getargvalues(frame)
        print(inspect.getframeinfo(frame))
        print(f'function name: {inspect.getframeinfo(frame).function}')
        for i in args:
            print(f"{i} = {values[i]}")

if __name__ == '__main__':
    p = Person()
    p.talk("zhangsan", 18, height=175)        

結果

Traceback(filename='D:/ProgramWorkspace/PythonNotes/00-Python-Essentials/demo.py', lineno=44, function='talk', code_context=['        print(inspect.getframeinfo(frame))\n'], index=0)
function name: talk
self = <__main__.Person object at 0x0000023E4CF17B08>
name = zhangsan
age = 18
height = 175

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