Closures and Loops in Python

Question

Possible Duplicate:
Lexical closures in Python

Suppose I have the following code

callbacks = []
for i in range(10):
  callbacks.append(lambda x: i)

all functions in callbacks will return the final value of i. How can I create callbacks that return the current value for i at creation time?

score 6 · Accepted Answer · answered Oct 23 '12 at 20:34

6

for i in range(10):
  callbacks.append(lambda x = i : x)

answered Oct 23 '12 at 20:34

gefei

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score 3 · Answer 2 · answered Oct 23 '12 at 20:36

3

In [113]: callbacks=[]

In [114]: for i in range(10):
    callbacks.append(lambda x=i:x**2)
   .....:     
   .....:     

In [117]: callbacks[0]()
Out[117]: 0

In [118]: callbacks[1]()
Out[118]: 1

In [119]: callbacks[2]()
Out[119]: 4

In [120]: callbacks[4]()
Out[120]: 16

answered Oct 23 '12 at 20:36

Ashwini Chaudhary

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I suppose you meant `lambda x=i: x`? – Fred Foo Oct 23 '12 at 20:38
@larsmans ah! yes, thanks for the catch. – Ashwini Chaudhary Oct 23 '12 at 20:41

Closures and Loops in Python

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