Python: How to invert a binary string without using loops in Python?

Question

I'm working on a project where I need to invert binary strings (i.e., change 0s to 1s and 1s to 0s). For example, if the input is "0110010", the output should be "1001101".

I'm looking for a solution that doesn't use Python loops (like for or while) for performance reasons. I've tried using a list comprehension, but I'm wondering if there's a more efficient way to do this.

Here's what I've tried so far:

s = "0110010"
s = "".join('1' if bit == '0' else '0' for bit in s)
print(s)

Is there a more efficient way to solve this problem in Python?

stackoverflow.com/questions/3920494/… there is an answer a few down the page using maketrans. — nathan hayfield
– nathan hayfield, Commented Sep 7, 2017 at 18:19
Why do you even have a billion-character string of ones and zeros? — user2357112
– user2357112, Commented Sep 7, 2017 at 18:19

Rohit-Pandey · Accepted Answer · 2017-09-07 18:26:21Z

4

The simple way by use swapping:

st = "0110010"
st=st.replace("0","a")
st=st.replace("1","0")
st=st.replace("a","1")
print (st)

answered Sep 7, 2017 at 18:26

Rohit-Pandey

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3 Comments

RobertB Over a year ago

This is useful, but it requires 3 loops through the string. This can be done in one loop using the the comprehension idea I posted in a separate answer.

user2357112 Over a year ago

@RobertB: The comprehension is a Python-level loop, though, so it has a lot more overhead than the C-level loop inside replace. The comprehension doesn't actually win the timing.

RobertB Over a year ago

Nice. Intuition proved me wrong... dang interpreter ;)

Jacob Garby · Accepted Answer · 2017-09-07 18:29:53Z

3

How to do this with either strings or binary literals.

Easy, use a bitwise operator. This is the proper way to do it, because it's useful to understand how to use these operators in Python. If this is a task, this seems like the way whoever set the task wanted it to be done.

# Make binary literal (0b prefix)
b = 0b11001001
# And use the complement operator
print(~b)

#Or if you want to print out the binary, try
print(bin(~b))

Here are some examples:

>>> ~0b110011
-52
>>> bin(~0b110001)
'-0b110010'
>>> bin(~0b11000)
'-0b11001'

If your binary number is a string:

s = "101"
# bin(~int(s,2)) = "010"

Note, you might want to trim the first three characters off of the space if you want just the binary characters, e.g.

bin(~int(s,2))[3:]

edited Sep 7, 2017 at 18:29

answered Sep 7, 2017 at 18:25

Jacob Garby

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1 Comment

Avo Asatryan Over a year ago

but i have strings, could you show ways how to convert string to bin , and bin to string?

RobertB · Accepted Answer · 2017-09-07 18:33:44Z

1

''.join('1' if x == '0' else '0' for x in '0110010')

answered Sep 7, 2017 at 18:33

RobertB

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Comments

J Johnson · Accepted Answer · 2017-09-07 18:32:12Z

0

This piece of code works with strings, try it:

>>> from string import maketrans
>>>
>>> initial_string = "10101010100011010"
>>> converted_string = initial_string.translate(maketrans("10","01"))

>>> converted_string    # The result is
'01010101011100101'
>>>

edited Sep 7, 2017 at 18:32

answered Sep 7, 2017 at 18:25

J Johnson

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