I have an array of functions, for example:
>>> def f():
... print "f"
...
>>> def g():
... print "g"
...
>>> c=[f,g]
Then i try to create two lambda functions:
>>> i=0
>>> x=lambda: c[i]()
>>> i+=1
>>> y=lambda: c[i]()
And then, call them:
>>> x()
g
>>> y()
g
Why c[i] in lambda are the same?
That's because the lambda function is fetching the value of the global variable i at runtime:
>>> i = 0
>>> x=lambda z = i : c[z]() #assign the current value of `i` to a local variable inside lambda
>>> i+=1
>>> y =lambda z = i : c[z]()
>>> x()
f
>>> y()
g
A must read: What do (lambda) function closures capture?
createAdder function at the end of stackoverflow.com/a/2295368/25050.In Python closures don't capture actual values, but instead they capture namespaces. So when you use i inside your function it's actually looked up in the enclosing scope. And the value there has already changed.
You don't need all those lambdas and lists to see this.
>>> x = 1
>>> def f():
... print(x)
...
>>> x = 2
>>> def g():
... print(x)
...
>>> g()
2
>>> f()
2
lambdas in the first place. Just replace those two lines withx = c[i]andy = c[i], and you will get exactly the functions you wanted. The only reason to ever writelambda: f()instead offis to stickfinto a closure namespace to look it up later, instead of just using it. You don't want to do that here, and in fact that's exactly what's causing your problem.