What is the most pythonic way of replacing values in nested lists?

Question

I have a list of strings, and I want to replace each 'X' and 'O' with True and False - turning each string into a list of booleans.

arr = ['XOOXO',
       'XOOXO',
       'OOOXO',
       'XXOXO',
       'OXOOO']

temp_list = []
bool_lists =[]

for str in arr:
    for char in str:
        if char == "X":
            temp_list.append(True)
        else:
            temp_list.append(False)
    bool_lists.append(temp_list)
    temp_list = []

This fills up the temp_list variable with booleans, appends the temp_list to the bool_lists variable, then empties the temp_list variable before starting on the next row.

The code above works, but I feel like there must be a more straightforward, pythonic way of doing this.

Example: `bools = [c == "X" for c in "XOOXO"]` yields `[True, False, False, True, False]`. Extend for the `arr` list. — jarmod, Mar 21 '23 at 13:55
`bool_lists = [[char == 'X' for char in string] for string in arr]` — Guy, Mar 21 '23 at 13:57
See the linked duplicate. Problems like this are a natural fit for list comprehensions. Use the technique twice: for the code the produces a "row" of booleans from a single string, and again to apply that code to each string in the overall list. — Karl Knechtel, Mar 21 '23 at 14:00
Thank you everyone, I knew it probably had to do something with dict/list comprehension, and I looked around but couldn’t find it. Thanks for pointing it out! — Mark Boyd, Mar 21 '23 at 17:48

Timur Shtatland · Accepted Answer · 2023-03-21T14:09:06.053

1

Use dictionaries and list comprehension like so:

dct = {'X': True, 'O': False}
bool_lists = [[dct[c] for c in s] for s in arr]
print(bool_lists)
# [[True, False, False, True, False], [True, False, False, True, False], [False, False, False, True, False], [True, True, False, True, False], [False, True, False, False, False]]

edited Mar 21 '23 at 14:09

answered Mar 21 '23 at 14:02

Timur Shtatland

12,024
2
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score 0 · Answer 2 · answered Mar 21 '23 at 14:03

0

Try this way, it's more sample

[[{"X":True,"O":False}.get(col, col)  for col in row] for row in arr]

answered Mar 21 '23 at 14:03

抓老鼠的猪

66
4

Thank you! I need to check out the `.get()` method thanks for bringing that to my attention. – Mark Boyd Mar 21 '23 at 17:45

What is the most pythonic way of replacing values in nested lists?

2 Answers2