将字符串列表列表转换为 int 列表列表

Question

I have read data from a comma-delimited text file( original format alpha_char,space 1,2,3,4,5,6,7, space alpha_characters newline char) and have output of [['1,2,3,4,5,6,7'],['7,5,3,9,8,2,4'], etc] ( ie lists of one string) and wish to convert these to [[1,2,3,4,5,6,7],[7,5,3,9,8,2,4], etc] ( ie lists of int). I would therefore appreciate advice on how to read the data from the text file into list of lists of int or how to convert what I have, list of lists of string to list of lists of int. I am being very stupid here, I know.

Answer 1

Using list comprehension:

>>> with open('file.txt') as f:
...     rows = [line.strip().split(',') for line in f]
...
>>> rows
[['1', '2', '3', '4', '5', '6', '7'], ['7', '5', '3', '9', '8', '2', '4']]
>>> nums = [list(map(int, row)) for row in rows]
>>> nums
[[1, 2, 3, 4, 5, 6, 7], [7, 5, 3, 9, 8, 2, 4]]

---

You can also use csv module :

>>> import csv
>>>
>>> with open('file.txt') as f:
...     reader = csv.reader(f)
...     rows = [row for row in reader]
...
>>> rows
[['1', '2', '3', '4', '5', '6', '7'], ['7', '5', '3', '9', '8', '2', '4']]

Answer 2

To filter numbers and convert your output, you can do the following:

new_list = [ [ int(x) for x in convert_list.split(",") if x.isdigit() ] for sublist in oldlist for convert_list in sublist ]

If you want to know if you have input which is not a number, you can omit the .isdigit() and use try except:

try:
    [ [ int(x) for x in convert_list.split(",") ] for sublist in oldlist for convert_list in sublist ]
except ValueError:
    print("bad input")