Change certain index value of string in a list-CodePudding

['0011111', '0011101', '0011110', '0011110', '0011100', '0010111', '0011000', '0011011', '0011000', '0010001', '0010100', '0010111', '0010110', '0010010', '0001110', '0001110', '0001010', '0001111', '0000111', '0001001', '0000101', '0001000', '0000100', '1000001']

Hi newbie here, how can I change the first index string value "1" in the List, example "1000001" to "0000001". Thanks for solution

CodePudding user response：

If I understand you correctly, if first character of the string in the list is 1, change it to 0:

lst = [
    "0001000",
    "0000100",
    "1000001",
]

lst = [f"0{s[1:]}" if s.startswith("1") else s for s in lst]
print(lst)

Prints:

["0001000", "0000100", "0000001"]

EDIT: Using str.replace:

lst = [s.replace("1", "0", 1) if s.startswith("1") else s for s in lst]
print(lst)

EDIT 2: If you want to change first 1 to 0 (regardless if 1 is found on first place or not you can do):

lst = [
    "0001000",
    "0000100",
    "1000001",
]

lst = [s.replace("1", "0", 1) for s in lst]
print(lst)

Prints:

['0000000', '0000000', '0000001']

CodePudding user response：

Considering that all those strings are binary representations 07bit (maximum value: 127 (0x7F, 0b01111111)), you could do (for each element):

Convert it to an base 2 (unsigned) integer
Bit operation - clearing the MSB is equivalent to anding with 63 (0x3F, 0b00111111)
Convert the resulting integer back to (base 2) string

>>> # Original list
>>> l7b = ["0011111", "0011101", "0011110", "0011110", "0011100", "0010111", "0011000", "0011011", "0011000", "0010001", "0010100", "0010111", "0010110", "0010010", "0001110", "0001110", "0001010", "0001111", "0000111", "0001001", "0000101", "0001000", "0000100", "1000001"]
>>> l7b_msb_cleared = [f"{int(e, 2) & 0x3F:07b}" for e in l7b]
>>> l7b_msb_cleared
['0011111', '0011101', '0011110', '0011110', '0011100', '0010111', '0011000', '0011011', '0011000', '0010001', '0010100', '0010111', '0010110', '0010010', '0001110', '0001110', '0001010', '0001111', '0000111', '0001001', '0000101', '0001000', '0000100', '0000001']
>>>
>>> [e == l7b[i] for i, e in enumerate(l7b_msb_cleared)]
[True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, True, False]