Prevent Variable Referencing - Printable Version

Prevent Variable Referencing - Printable Version

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Prevent Variable Referencing - Th3Eye - Oct-03-2018

I don't know how to explain it very well, but I've been trying to figure this out for a few days and I haven't had any luck with fixing it.

The following code is supposed to append a lambda to a list, so that the function the lambda calls can be called later on. NOTE: this isn't my actual code, but a proof of concept that works in the same way.

def foo(bar):
	print(bar)

li = []

for i in range(10):
	li.append(lambda: foo(i))

Later I can call the functions using this chunk of code.

for func in li:
	func()

When I run this, instead of steadily incrementing, it just uses the last value of i.

Output:9
9
9
9
9
9
9
9
9
9

I understand that this is due to how python handles variable referencing, but I want to know if there is a way to bypass this and only get the value of i without referencing it.

RE: Prevent Variable Referencing - ichabod801 - Oct-03-2018

You do this by having a function return a function.

def foo(bar):
    def sub():
        print(bar)
    return sub
 
li = []
 
for i in range(10):
    li.append(foo(i))

RE: Prevent Variable Referencing - buran - Oct-03-2018

from functools import partial
def foo(bar):
    print(bar)
 
li = []
 
for i in range(10):
    li.append(partial(foo, i))

for func in li:
    func()

Output:0
1
2
3
4
5
6
7
8
9

but it's weird what you are doing

RE: Prevent Variable Referencing - Th3Eye - Oct-03-2018

(Oct-03-2018, 04:56 PM)buran Wrote:

from functools import partial
def foo(bar):
    print(bar)
 
li = []
 
for i in range(10):
    li.append(partial(foo, i))

for func in li:
    func()

Output:0
1
2
3
4
5
6
7
8
9

but it's weird what you are doing

Can you explain what partial() does?

RE: Prevent Variable Referencing - buran - Oct-03-2018

(Oct-03-2018, 06:58 PM)Th3Eye Wrote: Can you explain what partial() does?

Check the docs for functools.partial()