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Analysis of common functions in the functools module in Python

Mar 01, 2017 pm 01:50 PM

functools python

1.partial

The first is the partial function, which can rebind the optional parameters of the function and generate a callable partial object:

&gt;&gt;&gt; int(&#39;10&#39;) # 实际上等同于int(&#39;10&#39;, base=10)和int(&#39;10&#39;, 10) 
10 
&gt;&gt;&gt; int(&#39;10&#39;, 2) # 实际上是int(&#39;10&#39;, base=2)的缩写 
2 
&gt;&gt;&gt; from functools import partial 
&gt;&gt;&gt; int2 = partial(int, 2) # 这里我没写base，结果就出错了 
&gt;&gt;&gt; int2(&#39;10&#39;) 
Traceback (most recent call last): 
 File &quot;&lt;stdin&gt;&quot;, line 1, in &lt;module&gt; 
TypeError: an integer is required 
&gt;&gt;&gt; int2 = partial(int, base=2) # 把base参数绑定在int2这个函数里 
&gt;&gt;&gt; int2(&#39;10&#39;) # 现在缺省参数base被设为2了 
2 
&gt;&gt;&gt; int2(&#39;10&#39;, 3) # 没加base，结果又出错了 
Traceback (most recent call last): 
 File &quot;&lt;stdin&gt;&quot;, line 1, in &lt;module&gt; 
TypeError: keyword parameter &#39;base&#39; was given by position and by name 
&gt;&gt;&gt; int2(&#39;10&#39;, base=3) 
3 
&gt;&gt;&gt; type(int2) 
&lt;type &#39;functools.partial&#39;&gt;

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As can be seen from this, the only thing to note is that the optional parameter must write the parameter name.

2.update_wrapper
Then there is the update_wrapper function, which can copy the __name__, __module__, __doc__ and __dict__ of the encapsulated function to the encapsulating function:

#-*- coding: gbk -*- 
 
def thisIsliving(fun): 
 def living(*args, **kw): 
  return fun(*args, **kw) + &#39;活着就是吃嘛。&#39; 
 return living 
 
@thisIsliving 
def whatIsLiving(): 
 &quot;什么是活着&quot; 
 return &#39;对啊，怎样才算活着呢？&#39; 
 
print whatIsLiving() 
print whatIsLiving.__doc__ 
 
print 
 
from functools import update_wrapper 
def thisIsliving(fun): 
 def living(*args, **kw): 
  return fun(*args, **kw) + &#39;活着就是吃嘛。&#39; 
 return update_wrapper(living, fun) 
 
@thisIsliving 
def whatIsLiving(): 
 &quot;什么是活着&quot; 
 return &#39;对啊，怎样才算活着呢？&#39; 
 
print whatIsLiving() 
print whatIsLiving.__doc__

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Result:

对啊，怎样才算活着呢？活着就是吃嘛。
None

对啊，怎样才算活着呢？活着就是吃嘛。
什么是活着

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But it’s not much use, after all, it’s just a little Just wrote 4 lines of assignment statements.

3.wraps
Then there is the wraps function, which also encapsulates update_wrapper:

#-*- coding: gbk -*- 
 
from functools import wraps 
 
def thisIsliving(fun): 
 @wraps(fun) 
 def living(*args, **kw): 
  return fun(*args, **kw) + &#39;活着就是吃嘛。&#39; 
 return living 
 
@thisIsliving 
def whatIsLiving(): 
 &quot;什么是活着&quot; 
 return &#39;对啊，怎样才算活着呢？&#39; 
 
print whatIsLiving() 
print whatIsLiving.__doc__

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The result is still the same:

对啊，怎样才算活着呢？活着就是吃嘛。
什么是活着

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4.total_ordering
Finally, the total_ordering function gives a rich sorting method, using decorators simplifies operations. If used, a __lt__(), __le__(), __gt__(), or __ge__() must be defined in the class. An __eq__() method should be added to the class.

from functools import total_ordering

@total_ordering
class Student(object):
  def __init__(self, name):
    self.name = name

  def __eq__(self, other):
    return self.name.lower() == other.name.lower()

  def __lt__(self, other):
    return self.name.lower() &lt; other.name.lower()

a = Student(&#39;dan&#39;)
b = Student(&#39;mink&#39;)

print a &gt; b
print a
print sorted([b, a])

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Print results

False
&lt;__main__.Student object at 0x7f16ecb194d0&gt;
[&lt;__main__.Student object at 0x7f16ecb194d0&gt;, &lt;__main__.Student object at 0x7f16ecb195d0&gt;]

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