List Comprehension Issue

[johnywhy]

This works:

choices = 'a', 'b', 'c'
menu = ""

for idx, choice in enumerate(choices):
	menu += "\t".join((str(idx), choice, '\n'))

print(menu)
0	a
1	b
2	c

This doesn't:

choices = 'a', 'b', 'c'

menu = ["\t".join((str(idx), choice, '\n')) for idx, choice in enumerate(choices)]

print(menu)
['0\ta\t\n', '1\tb\t\n', '2\tc\t\n']

What am i doing wrong?

[sgrey]

This works:

choices = 'a', 'b', 'c'
menu = ""

for idx, choice in enumerate(choices):
	menu += "\t".join((str(idx), choice, '\n'))

print(menu)
0	a
1	b
2	c

This doesn't:

choices = 'a', 'b', 'c'

menu = ["\t".join((str(idx), choice, '\n')) for idx, choice in enumerate(choices)]

print(menu)
['0\ta\t\n', '1\tb\t\n', '2\tc\t\n']

What am i doing wrong?

join constructs a string, so what your first code does is string concatenation. List comprehension makes a list, so in your second code you are adding list elements to a list instead of making a string. You need to iterate over them and print them if that's what you want to do.

[johnywhy]

in your second code you are adding list elements to a list instead of making a string. You need to iterate over them and print them if that's what you want to do.

I want a joined string, as in expanded for statement. I thought the list comprehension version was identical to the first in behavior. What adjustment would i make to the list comprehension version to make to operationally identical to the normal for?

thx!

[sgrey]

in your second code you are adding list elements to a list instead of making a string. You need to iterate over them and print them if that's what you want to do.

I want a joined string, as in expanded for statement. I thought the list comprehension version was identical to the first in behavior. What adjustment would i make to the list comprehension version to make to operationally identical to the normal for?

thx!

List (or other type of) comprehension is a mechanism for creating lists (or other type of collections). Basically you cannot make a list comprehension behave in way that doesn't make a list. You basically have to call join on your list to make it a string. So you would do something like

items = ["\t".join((str(idx), choice)) for idx, choice in enumerate(choices)]
menu = "\n".join(items)

[johnywhy]

menu = "\n".join(items)

Or, wrap it in the join:

menu = "\n".join(["\t".join((str(idx), choice)) for idx, choice in enumerate(choices)])

A normal for might be easier to read :)

[Pedroski55]

I think this:

menu2 = ["\t".join((str(idx), choice, '\n')) for idx, choice in enumerate(choices)]

Does what it should do: it joins (str(idx), choice, '\n') with a \t between them, producing the list menu2, which is what a list comprehension should do:

Output:
['0\ta\t\n', '1\tb\t\n', '2\tc\t\n']

If you want a string from that list, just join it:

s = ''.join(menu2)

Output:
'0\ta\t\n1\tb\t\n2\tc\t\n'