Python中str()与__str__、repr()与__repr__、eval()、__unicode__的关系与区别
首先
先弄清楚str()与__str__、repr()与__repr__ 的区别,str()与repr()都是python中的内置函数,是直接用来格式化字符串的函数。而__str__与__repr__ 是在类(对象)中对类(对象)本身进行字符串处理。
其次
需要弄清楚str与repr之间的区别【引用】
python3
>>> help(str)
Help on class str in module builtins:
class str(object)
| str(object='') -> str
| str(bytes_or_buffer[, encoding[, errors]]) -> str
|
| Create a new string object from the given object. If encoding or
| errors is specified, then the object must expose a data buffer
| that will be decoded using the given encoding and error handler.
| Otherwise, returns the result of object.__str__() (if defined)
| or repr(object).
| encoding defaults to sys.getdefaultencoding().
| errors defaults to 'strict'.
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python2
class str(basestring)
| str(object='') -> string
|
| Return a nice string representation of the object.
| If the argument is a string, the return value is the same object.
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str【引用】
返回一个可以用来表示对象的可打印的友好的字符串
对字符串,返回本身。
没有参数,则返回空字符串
对类,可通过__str__()
成员控制其行为。该成员不存在,则使用其 __repr__()
成员。
与 repr 区别:不总是尝试生成一个传给 eval 的字符串,其目标是可打印字符串。
python3
>>> help(repr)
Help on built-in function repr in module builtins:
repr(obj, /)
Return the canonical string representation of the object.
For many object types, including most builtins, eval(repr(obj)) == obj.
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python2
repr(...)
repr(object) -> string
Return the canonical string representation of the object.
For most object types, eval(repr(object)) == object.
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repr【引用】
返回一个可以用来表示对象的可打印字符串
首先,尝试生成这样一个字符串,将其传给 eval()可重新生成同样的对象
否则,生成用尖括号包住的字符串,包含类型名和额外的信息(比如地址)
一个类(class)可以通过 __repr__()
成员来控制repr()函数作用在其实例上时的行为。
class a():
def __unicode__(self):
pass
def __str__(self):
pass
def __repr__(self):
pass
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>>> help(eval)
Help on built-in function eval in module builtins:
eval(source, globals=None, locals=None, /)
Evaluate the given source in the context of globals and locals.
The source may be a string representing a Python expression
or a code object as returned by compile().
The globals must be a dictionary and locals can be any mapping,
defaulting to the current globals and locals.
If only globals is given, locals defaults to it.
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>>> eval('1+2')
3
>>> str('1+2')
'1+2'
>>> repr('1+2')
"'1+2'"
>>> type(repr('1+2'))
<class 'str'>
>>> type(str('1+2'))
<class 'str'>
>>> type(eval('1+2'))
<class 'int'>
#就相当于上面说的eval(repr(object)) == object
>>> eval(repr('1+2'))
'1+2'
>>> '1+2'
'1+2'
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示例
#test2.py
class A(object):
def __str__(self):
return "__str__"
def __repr__(self):
return "__repr__"
a = A()
b = A
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>>> import test2
>>> test2.a
__repr__
>>> print(test2.a)
__str__
>>> test2.b
<class 'test2.A'>
>>> print(test2.b)
<class 'test2.A'>
转载:http://blog.csdn.net/foryouslgme/article/details/51658057