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Creating functions (or lambdas) in a loop (or comprehension) (7 answers)

Closed 12 months ago.

我有一份马提卜达职能清单,我想按顺序评估。我不肯定为什么,但只有最后一项职能得到评价。例如下:

  >>> def f(x,z):
  ...     print "x=",x,", z=",z
  ... 
  >>> 
  >>> g = lambda x : f(x,13)
  >>> g(2)
  x= 2 , z= 13    # As expected
  >>> 
  >>> lst=[]
  >>> 
  >>> for i in range(0,5): 
  ...    lst.append(lambda x: f(x,i))
  ... 
  >>> print lst
  [<function <lambda> at 0x10341e2a8>, <function <lambda> at 0x10341e398>, <function <lambda> at 0x10341e410>, <function <lambda> at 0x10341e488>, <function <lambda> at 0x10341e500>]
  >>> 
  >>> for fn in lst:
  ...   fn(3)
  ... 
  x= 3 , z= 4 # z should be 0
  x= 3 , z= 4 # z should be 1
  x= 3 , z= 4 # z should be 2
  x= 3 , z= 4 # z should be 3
  x= 3 , z= 4 # as expected.

我认为,只有最后一点已经执行,而不是其他。任何想法? 感谢!

Answer 1

伊斯兰堡只是研究一的全球价值。

而是:

for i in range(0,5):
  lst.append(lambda x, z=i: f(x,z))

Answer 2

• 为我努力使用部分工程:

from functools import partial

def f(x,z):
    print "x=",x,", z=",z

lst = [ partial(f,z=i) for i in range(5) ]

for fn in lst:
    fn(3)

Answer 3

不是一位专家,但可能的话,就是说,有人正在治疗i。页: 1

lst.append(lambda x: f(x,i))

作为参考吗? 其后,<代码>i等于其最后分配数值(4),当职能被指定时,则按其<代码>i参引、发现4并具有这一价值执行。

披露:可能不知。

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