Use for loop inside another for loop

Question

I'm trying to print a file in rainbow colors. But however I have a problem, here is my code:

color = [91, 93, 92, 96, 94, 95]

with open(sys.argv[1]) as f:
for i in f.read():
    for c in color:
        print('\033[{0}m{1}\033[{0};m'
              .format(c, i), end='', flush=True)

The question is, I want the output like this: Hello(H in red, e in yellow, etc. ), but I got the output like this:HHHHHeeeeellll...(first H in red, second H in yello, etc.).

I know that because the first for will loop the second for. But how can I solve this?

AChampion · Accepted Answer · 2015-09-12 06:21:44Z

2

You don't want to loop over the colours for each letter just cycle through the colours, you can use itertools.cycle to cycle through the colors just calling next() to get the next color:

from itertools import cycle
color = cycle([91, 93, 92, 96, 94, 95])

with open(sys.argv[1]) as f:
    for i in f.read():
       print('\033[{0}m{1}\033[{0};m'
             .format(next(color), i), end='', flush=True)

edited Sep 12, 2015 at 6:21

answered Sep 12, 2015 at 6:19

AChampion

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2 Comments

AChampion Over a year ago

It turns [1,2,3] into the infinite list [1,2,3,1,2,3,1,2,3,...] but without the overhead of creating the list (see generators)

Remi Guan Over a year ago

I understand, it will create a generator, and that turns [1,2,3] into [1,2,3,1,2,3,1,2,3,...] . Then we use next() to call it. right?

glglgl · Accepted Answer · 2015-09-12 06:22:37Z

1

You have to iterate them in a "zipping" way, possibly repeating the second one.

color = [91, 93, 92, 96, 94, 95]

with open(sys.argv[1]) as f:
    for i, c in itertools.izip(f.read(), itertools.cycle(color)):
        print('\033[{0}m{1}\033[{0};m'
          .format(c, i), end='', flush=True)

answered Sep 12, 2015 at 6:22

glglgl

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7 Comments

Remi Guan Over a year ago

hum, I got this error: AttributeError: 'module' object has no attribute 'izip'

AChampion Over a year ago

In python 3 you don't need itertools.izip just zip will do.

Remi Guan Over a year ago

It's working! and what's the difference between your answer and @achampion 's answer?

AChampion Over a year ago

Not much, both use cycle to create an infinite list of cycling colors, but this uses zip() to join the letter and color, vs. just calling next() on the cycle generator directly. zip() does the next() call for you but has a little more overhead because it creates a tuple which you unpack in the for loop.

AChampion Over a year ago

Just to be clear the overhead is minor and I would have no issue using either of these solutions, zip() is idiomatic when trying to deal with 2 lists at the same time.

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oliverpool · Accepted Answer · 2015-09-12 06:20:17Z

0

As you mention you shouldn't use a second for loop.

You can use a color_index (initial value: 0), and you increment it (modulo the number of colors) at every loop, and use it: color[color_index].

answered Sep 12, 2015 at 6:20

oliverpool

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