TypeError: can only concatenate str (not "bytes") to str

TypeError: can only concatenate str (not "bytes") to str #

The Python "TypeError: can only concatenate str (not "bytes") to str" occurs when we try to concatenate a string and a bytes object. 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_str = 'hello '

my_bytes = b'James Doe'

# ⛔️ TypeError: can only concatenate str (not "bytes") to str
result = my_str + my_bytes

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_str = 'hello '

my_bytes = b'James Doe'

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

print(result)  # 👉️ 'hello James Doe'

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_str = 'hello '

my_bytes = b'James Doe'

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

print(result)  # 👉️ b'hello James Doe'

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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my_str = 'hello'

# 👇️ decode bytes to str
my_bytes = b'James Doe'.decode('utf-8')

result = f'{my_str} {my_bytes}'

print(result)  # 👉️ "hello James Doe"

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

my_bytes = b'James Doe'
print(type(my_bytes))  # 👉️ <class 'bytes'>
print(isinstance(my_bytes, bytes))  # 👉️ 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.