Problem Formulation
If you print a binary number, Python uses the prefix '0b' to indicate that it’s a number in the binary system and not in the decimal system like normal integers.
print(bin(42)) # 0b101010
However, if you already know that the output numbers are binary, you don’t necessarily need the '0b' prefix.
How to print binary numbers without the '0b' prefix?
Method 1: Slicing
To skip the prefix, use slicing and start with index 2 on the binary string. For example, to skip the prefix '0b' on the result of x=bin(42)='0b101010', use the slicing operation x[2:] that results in just the binary number '101010' without the prefix '0b'.
x = bin(42) print(x) # 0b101010 print(x[2:]) # 101010
Feel free to dive into the bin() built-in function in this video tutorial:
But what if you actually want to replace the prefix '0b' with the prefix '00' so that the resulting string has the same length?
Method 2: Slicing + zfill()
The Python string.zfill() method fills the string from the left with '0' characters. In combination with slicing from the third character, you can easily construct a binary string without leading '0b' characters and with leading '0' characters up to the length passed into the string.zfill(length) method.
print(bin(42)[2:].zfill(8)) # 00101010
Alternatively, if you want to create a string with 12 characters, use string.zfill(12):
print(bin(42)[2:].zfill(12)) # 000000101010
You can learn more about zfill() in this video about Python string methods:
Method 3: Negative Binaries
If you need to handle negative binaries, the above methods do not work because the binary number now needs to replace the second and third character '0b'. For example, the binary number bin(-42) is '-0b101010'. You cannot simply skip the first two characters to obtain the correct result, can you? At the same time, if you always skipped or replaced the second and third characters, it wouldn’t work for positive numbers either. So what to do?
For a positive or negative binary to print it without the '0b' prefix or '-0b' prefix, you can simply use the string.replace() method and replace each occurrence of 'b' with '0'. The resulting string is mathematically correct because leading '0's don’t change the value of the number.
# Negative Binary
print(bin(-42).replace('b', '0'))
# -00101010
# Positive Binary
print(bin(42).replace('b', '0'))
# 00101010
You can learn more about the replacing functionality here:
Where to Go From Here?
Enough theory. Let’s get some practice!
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