Year 12s: what will be the first way you research your future options? >>

for loop in python

what does this for loop below actually do?

for i, x in enumerate(self.list):
.....

(edited 2 years ago)

i is the "index" for the list, x is the actual variable in the list

For example

for i, x in enumerate([a,b,c,d]):
print(i, x)

would print

0 a
1 b
2 c
3 d

Reply 2

Carrying a torch

Original post by Callicious

i is the "index" for the list, x is the actual variable in the list

For example

for i, x in enumerate([a,b,c,d]):
print(i, x)

would print

0 a
1 b
2 c
3 d

is there a way of producing the same outcome without the use of enumerate?

(edited 2 years ago)

Reply 3

Callicious

Original post by Carrying a torch

is there a way of producing the same outcome without the use of enumerate?

There's always a way, but why would you want to?

Reply 4

Carrying a torch

Original post by Callicious

There's always a way, but why would you want to?

It might better help me understand because I have not come across the use of 'enumerate' before, is it like range or len?

Reply 5

Callicious

Original post by Carrying a torch

It might better help me understand because I have not come across the use of 'enumerate' before, is it like range or len?

See https://towardsdatascience.com/python-enumerate-built-in-function-acccf988d096

Personally I find it invaluable when working with loops- it's useful for calling to lists separate from the one you're iterating through that may have the same indices as the one you're iterating through.

Reply 6

Carrying a torch

Original post by Callicious

Still not sure how the same could be achieved without enumerate but I think that clarifies a lot

Reply 7

Callicious

Original post by Carrying a torch

Still not sure how the same could be achieved without enumerate but I think that clarifies a lot

I mean, before I learned about enumerate() and zip() I usually just did something like

list = example_list
indices = np.arange(0, len(list), 1)
for num in indices:
x_num = list[num]

Alternatively just use

for num in range(len(indices)):
etc etc

You've got options aside from enumerate- it's just way more convenient and easier.

Reply 8

Composure

Original post by Carrying a torch

is there a way of producing the same outcome without the use of enumerate?

enumerate() is a function... it behaves like any other function you've come across. Its name is actually really descriptive of what it does; it enumerates the elements within an iterable (e.g a list, a tuple, a string). This is the code for enumerate(), it's really simple:


def enumerate(sequence, start=0):
    n = start
    for elem in sequence:
        yield n, elem
        n += 1

When you use enumerate() in a for loop, it removes the need for having to code your own counter. See for youself what it does by entering enumerate(["a", "b", "c", "d"]) into IDLE Shell.

(edited 2 years ago)