TypeError: a bytes-like object is required, not 'str'

TypeError: a bytes-like object is required, not 'str'

To solve the Python "TypeError: a bytes-like object is required, not str", encode the str to bytes, e.g. my_str.encode('utf-8'). The str.encode method returns an encoded version of the string as a bytes object. The default encoding is utf-8.

Here is an example of how the error occurs.

# 👇️ open file
with open('example.txt', 'rb') as f:
    result = f.readlines()

    # ⛔️ TypeError: a bytes-like object is required, not 'str'
    if 'first line' in result[0]:
        print('success')

We opened the file in binary mode (using the rb mode), so the result list contains bytes objects.

To solve the error, use the encode() method to encode the str into bytes.

with open('example.txt', 'rb') as f:
result = f.readlines()

    # 👇️ call encode() on the string
    if 'first line'.encode('utf-8') in result[0]:
        # ✅ this runs
        print('success')

Now the values on both sides of the in operator are bytes objects, so the error is resolved.

Note that we could have also decoded the bytes object into a string.

with open('example.txt', 'rb') as f:
result = f.readlines()

    # ✅ decode bytes into str
    if 'first line' in result[0].decode('utf-8'):
        print('success')

The values on the left and right-hand side of the in operator are of the same type (str).

The bytes.decode method returns a string decoded from the given bytes. The default encoding is utf-8.

You can also use a list comprehension to perform the operation on each element in a list.

with open('example.txt', 'rb') as f:
    lines = [l.decode('utf-8') for l in f.readlines()]

    if 'first line' in lines[0]:
        print('success')

Conclusion

To solve the Python "TypeError: a bytes-like object is required, not str", encode the str to bytes, e.g. my_str.encode('utf-8'). The str.encode method returns an encoded version of the string as a bytes object. The default encoding is utf-8.