TypeError: can't concat str to bytes in Python

TypeError: can't concat str to bytes in Python #

The Python "TypeError: can't concat str to bytes" occurs when we try to concatenate a bytes object and a string. To solve the error, decode the bytes object into a string before concatenating the strings.

Here is an example of how the error occurs.

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my_bytes = b'hello '

my_str = 'world'

# ⛔️ TypeError: can't concat str to bytes
result = my_bytes + my_str

The values on the left and right-hand sides need to be of compatible types.

One way to solve the error is to convert the bytes object to a string.

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my_bytes = b'hello '

my_str = 'world'

# 👇️ decode bytes object
result = my_bytes.decode('utf-8') + my_str

print(result)  # 👉️ "hello world"

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

Alternatively, you can encode the string to a bytes object.

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my_bytes = b'hello '

my_str = 'world'

result = my_bytes + my_str.encode('utf-8')

print(result)  # 👉️ b"hello world"

The str.encode method returns an encoded version of the string as a bytes object. The default encoding is utf-8.

Once you convert the bytes object to a string, you can use formatted string literals.

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# 👇️ decode bytes object
my_bytes = b'hello '.decode('utf-8')

my_str = 'world'

result = f'{my_bytes} {my_str}'

print(result)  # "hello  world"

Make sure to wrap expressions in curly braces - {expression}.

If you aren't sure what type a variable stores, use the built-in type() class.

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# 👇️ decode bytes object
my_bytes = b'hello '
print(type(my_bytes))  # 👉️ <class 'bytes'>
print(isinstance(my_bytes, bytes))  # 👉️ True

my_str = 'world'
print(type(my_str))  # 👉️ <class 'str'>
print(isinstance(my_str, str))  # 👉️ True

The type class returns the type of an object.

The isinstance function returns True if the passed in object is an instance or a subclass of the passed in class.

Conclusion #

The Python "TypeError: can't concat str to bytes" occurs when we try to concatenate a bytes object and a string. To solve the error, decode the bytes object into a string before concatenating the strings.