Use the ast module

>>> import ast
>>> list_as_string = "['item 1', 'item 2', 'item 3']"
>>> _list = ast.literal_eval(list_as_string)
>>> _list
['item 1', 'item 2', 'item 3']
>>>

To "convert" a string to a list, you can just place it in one, e.g., by creating a new list with []:

input1 = 'I am a boy'
output1 = [input1]

To "convert" a list like you have to a string, you could simply extract the first and only value in it:

input2 = ['I am a boy']
output2 = input2[0]

Make a list(your_string).

>>> s = "mep"
>>> list(s)
['m', 'e', 'p']

If the string looks like a syntactically valid Python list, then you can get that list data by calling ast.literal_eval:

>>> import ast
>>> s = "[[451166.32,719761.36,20.37,0.06,],[451162.97,719765.06,20.41,0.048,1],[451161.63,719766.54,10.17,0.048,],[451158.26,719770.23,20.44,0.048,],[451156.19,719772.54,20.05,0.048,0],[451148.7,719780.68,-10.77,0.048,],[451138.57,719791.95,-10.2,0.048,],[451129.33,719802.15,-10.38,0.048,],[451118.07,719814.56,10.06,0.048,],[451105.98,719827.91,-10.64,0.048,],[451095.10,719839.91,-10.47,0.048,],[451087.17,719848.66,-10.72,0.048,],[451082.94,719853.31,10.92,0.048,0],[451078.,719858.77,2.75,10.048,],[451076.79,719860.10,5.2,10.06,1]]"
>>> x = ast.literal_eval(s)
>>> type(x)
<class 'list'>
>>> x
[[451166.32, 719761.36, 20.37, 0.06], [451162.97, 719765.06, 20.41, 0.048, 1], [451161.63, 719766.54, 10.17, 0.048], [451158.26, 719770.23, 20.44, 0.048], [451156.19, 719772.54, 20.05, 0.048, 0], [451148.7, 719780.68, -10.77, 0.048], [451138.57, 719791.95, -10.2, 0.048], [451129.33, 719802.15, -10.38, 0.048], [451118.07, 719814.56, 10.06, 0.048], [451105.98, 719827.91, -10.64, 0.048], [451095.1, 719839.91, -10.47, 0.048], [451087.17, 719848.66, -10.72, 0.048], [451082.94, 719853.31, 10.92, 0.048, 0], [451078.0, 719858.77, 2.75, 10.048], [451076.79, 719860.1, 5.2, 10.06, 1]]

I'm not completely sure, but it sounds like your string might actually look like multiple lists concatenated together, in which case you can't just call literal_eval on it:

>>> import ast
>>> s = "[1,2][3,4,[[5,6],7]][8,9]"
>>> ast.literal_eval(s)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Programming\Python 3.6\lib\ast.py", line 85, in literal_eval
    return _convert(node_or_string)
  File "C:\Programming\Python 3.6\lib\ast.py", line 84, in _convert
    raise ValueError('malformed node or string: ' + repr(node))
ValueError: malformed node or string: <_ast.Subscript object at 0x02E25650>

If this is the case, you can separate your data into individual groups so you can eval them independently.

import ast

def separate_groups(s):
    """finds matching square brackets within `s` and yields successive portions that resemble valid list literals.
    note: may not operate correctly on data that contains quoted brackets, for example `"[1, '[', 2][3,4]"`
    """
    depth = 0
    last_seen_group_end = -1
    for i,c in enumerate(s):
        if c == "[":
            depth += 1
        elif c == "]":
            depth -= 1
            if depth == 0:
                yield s[last_seen_group_end+1: i+1]
                last_seen_group_end = i

s = "[1,2][3,4,[[5,6],7]][8,9]"
result = [ast.literal_eval(group) for group in separate_groups(s)]
print(result)

Result:

[[1, 2], [3, 4, [[5, 6], 7]], [8, 9]]