python 語法 內置函數 hasattr getattr setattr dir

參考： https://docs.python.org/3/library/functions.html?highlight=hasattr#getattr

 

例子1：針對類TestA 作屬性操做

class TestA:
    def fun_1(self):
        print "fun_1"

    def fun_2(self):
        print "fun_2"

def fun_2():
    print "fun_3"

test_a = TestA()
print hasattr(test_a, "fun_1")

fun_a = getattr(test_a,"fun_2")
print fun_a
fun_a()

setattr(test_a,"fun_2",fun_2) #對原有函數進行了覆蓋。熱更新代碼經常使用
test_a.fun_2()
print dir(TestA)

　　結果：

True
<bound method TestA.fun_2 of <__main__.TestA instance at 0x0000000002E70E88>>
fun_2
fun_3
['__doc__', '__module__', 'fun_1', 'fun_2']

　　

例子2：針對一個文件內的屬性進行條件篩選：

首先建立新測試文件test_file.py：

A="a.b"
class B:
    def fun_1(self):
        pass
C=[1,2]
D="png.a"
E="cc.ee"

而後對文件進行邏輯處理：

# coding=utf-8


import test_file

# 刪選出test_file中全部的str、內有.、不含有png的
str_list = []
for item in dir(test_file):  # 查詢文件下的屬性名
    value = getattr(test_file, item)  # 查詢屬性名的具體值
    if type(value) != str:
        continue
    if value.find('.') < 0 or value.find('png') >= 0:
        continue
    str_list.append(value)

for item in str_list:
    print item

結果：

a.b
cc.ee

 

總結：

setattr(object, name, value)

This is the counterpart of getattr(). The arguments are an object, a string and an arbitrary value. The string may name an existing attribute or a new attribute. The function assigns the value to the attribute, provided the object allows it. For example, setattr(x, 'foobar', 123) is equivalent to x.foobar = 123.

setattr會進行屬性覆蓋，代碼熱更可使用。

 

dir([object])

Without arguments, return the list of names in the current local scope. With an argument, attempt to return a list of valid attributes for that object.

If the object has a method named __dir__(), this method will be called and must return the list of attributes. This allows objects that implement a custom __getattr__() or __getattribute__() function to customize the way dir() reports their attributes.

If the object does not provide __dir__(), the function tries its best to gather information from the object’s __dict__ attribute, if defined, and from its type object. The resulting list is not necessarily complete, and may be inaccurate when the object has a custom __getattr__().

The default dir() mechanism behaves differently with different types of objects, as it attempts to produce the most relevant, rather than complete, information:

• If the object is a module object, the list contains the names of the module’s attributes.
• If the object is a type or class object, the list contains the names of its attributes, and recursively of the attributes of its bases.
• Otherwise, the list contains the object’s attributes’ names, the names of its class’s attributes, and recursively of the attributes of its class’s base classes.

The resulting list is sorted alphabetically. For example:

>>>

>>> import struct >>> dir() # show the names in the module namespace ['__builtins__', '__name__', 'struct'] >>> dir(struct) # show the names in the struct module ['Struct', '__all__', '__builtins__', '__cached__', '__doc__', '__file__',  '__initializing__', '__loader__', '__name__', '__package__',  '_clearcache', 'calcsize', 'error', 'pack', 'pack_into',  'unpack', 'unpack_from'] >>> class Shape: ... def __dir__(self): ... return ['area', 'perimeter', 'location'] >>> s = Shape() >>> dir(s) ['area', 'location', 'perimeter'] 

Note

 

Because dir() is supplied primarily（首要的） as a convenience for use at an interactive prompt(敏捷交互？), it tries to supply an interesting set of names more than it tries to supply a rigorously or consistently defined set of names, and its detailed behavior may change across releases. For example, metaclass attributes are not in the result list when the argument is a class.

dir返回有意義的屬性集合，而不是全部屬性