Turning a for loop with multiple conditionals into a comprehension

Question

def presses(phrase):
    i = 0
    for char in phrase.upper():
        if char in '1ADGJMPTW*#':
            i += 1
        if char.isspace() == True:
            i += 1
        if char in 'BEHKNQUX0':
            i += 2
        if char in 'CFILORVY':
            i += 3
        if char in '23456S8Z':
            i += 4
        if char in '79':
            i += 5
    return i

I've recently completed a python puzzle in an attempt to better my scripting ;however, I've tried turning my loop into a comprehension, but I'm having trouble doing this because of all the conditionals. Can anyone help me try and turn this loop into a comprehension?

I think this question has a few useful answers and some helpful discussion to dissect the answers. — gallen
– gallen, Commented Jun 29, 2020 at 22:22
Why do you want to turn this into a comprehension construct? Those produce various containers or generators, you are simply counting things and returning an int... Given the structure of what you are doing, it's going to be much cleaner as a regular for-loop. — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Jun 29, 2020 at 22:23
Does this answer your question? Multiple IF conditions in a python list comprehension — adamgy
– adamgy, Commented Jun 29, 2020 at 22:24
A list comprehensions is for creating a list. A dict comprehensions is for creating a dict. You're calculating an int. There's no such thing as an int comprehension. — khelwood
– khelwood, Commented Jun 29, 2020 at 22:24
@adamgy not really comparable, conditional expressions arequire an if-else, not various ifs, at least, it won't be semantically equivalent. — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Jun 29, 2020 at 22:24

caring-goat-913 · Accepted Answer · 2020-06-29 22:33:42Z

1

If your increment rules are based on simple strings, then I would create a lookup table and iterate over your input string:

lookup = {
    '1': 1,
    'A': 1,
    ...
    '7': 5,
    '9': 5,
}

output = sum(lookup[char] for char in phrase)

answered Jun 29, 2020 at 22:33

caring-goat-913

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ori6151 · Accepted Answer · 2020-06-29 22:37:37Z

1

To add to @trianta2, if you don't want a lookup dictionary (for some reason), you can do this:

def presses_v2(phrase):
    return sum(1 if c in '1ADGJMPTW*# \t' else 2 if c in 'BEHKNQUX0' else 3 if c in 'CFILORVY' else 4 if c in '23456S8Z' else 5 if c in '79' else 0 for c in phrase.upper())

Note that your 2nd if-statement can be included in the first:

if char in '1ADGJMPTW*# \t':
    i += 1

I also changed char to c, to make the line shorter.

answered Jun 29, 2020 at 22:37

ori6151

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Saelyth · Accepted Answer · 2020-06-29 22:51:34Z

0

I don't get why would you want a list comprehension of this, since your code is easier to understand as you have it now, but.... I would try this way, it's messy but it works.

i = [z for x, z in [('1ADGJMPTW*#', 1), (" ", 1), ('BEHKNQUX0', 2), ('CFILORVY', 3), ('23456S8Z', 4), ('79', 5)] for char in phrase.upper() if char in x]

It's based on the logic that every IF that you have can be divided into 2 parts of a tuple, the condition and the result, knowing that you just have to build a list of tuples and iteract it. It gives you a list of the value of each character.

If you want the total, just sum it:

i = sum([z for x, z in [('1ADGJMPTW*#', 1), (" ", 1), ('BEHKNQUX0', 2), ('CFILORVY', 3), ('23456S8Z', 4), ('79', 5)] for char in phrase.upper() if char in x])

edited Jun 29, 2020 at 22:51

answered Jun 29, 2020 at 22:40

Saelyth

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