如何将不带逗号的字符串解析为 python 列表？

Question

I want to parse a string like this to a python list:

"[[ 3.14  2.12] [1.11 2.22 ] [10.0 12.0]]"    # Not separated by comma

I tried to use eval() function, but it failed with invalid syntax. Is there another way to easily parse such a string into python list?

What I hope to achieve is to obtain a real python list like this:

mylist = [[ 3.14,  2.12], [1.11, 2.22 ], [10.0, 12.0]]

and mylist[0] will return [3.14, 2.12] and mylist[0][1] will return 2.12.

Answer 1

This simply replaces the empty spaces with comma and then using the ast module you can convert a string represtntaion of lists of list into list.

import ast
h = "[[3.14 2.12] [1.11 2.22] [10.0 12.0]]"
a = str(h).replace( ' ' , ',' )
x = ast.literal_eval(a)
print(x)

Output

[[3.14, 2.12], [1.11, 2.22], [10.0, 12.0]] # of type lists of list

Also, note that this is rather a naive approach since this requires the string representation of lists of the list to be in the correct format.

Eg this is valid [[3.14 2.12] [1.11 2.22] [10.0 12.0]] ,whereas [[ 3.14 2.12] [1.11 2.22 ] [10.0 12.0]] this is not due to the presence of empty spaces here [[ 3.14] for example.

Answer 2

re.sub can be used to add a comma after each nested list and number.

import re

s = "[[ 3.14  2.12] [1.11 2.22 ] [10.0 12.0]]"

def add_comma(match):
    return match.group(0) + ','

s = re.sub(r'\[[0-9\.\s]+\]', add_comma, s)
s = re.sub(r'([0-9\.]+)', add_comma, s)
mylist = eval(s)

Answer 3

x= "[[3.14 2.12] [1.11 2.22] [10.0 12.0]]"
z=[y.strip().split(']')[0].split(' ') for y in x.split('[') if y!='']

Explanation: Splitting x on

'[' produces-->['', '', '3.14 2.12] ', '1.11 2.22] ', '10.0 12.0]]']

Using condition if y!='' on this split produces

['3.14 2.12] ', '1.11 2.22] ', '10.0 12.0]]']

Using y.strip() removes the extra whitespaces in the end of each element. Stripping on ']' produces

 [['3.14 2.12', ''], ['1.11 2.22', ''], ['10.0 12.0', '', '']]

Now, as we can see only the 1st element has our values, take index =0 & split on '' produces

 [['3.14', '2.12'], ['1.11', '2.22'], ['10.0', '12.0']]