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

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# 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.

typeerror typeerror bytes like object is required not str

If you got the error when using the socket module, scroll down to the next section.

Here is an example of how the error occurs.

main.py

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# 👇️ Open the 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.

The error is caused because we can't check if a string is contained in a bytes object as the two values are of different types.

# Encode the string into bytes to solve the error

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

main.py

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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')

encode string into bytes to solve the error

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

# Decoding the bytes object into a string

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

main.py

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

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

decoding the bytes object into string

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.

main.py

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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')

The example shows how to decode each bytes object in the list to a string.

# Solve the error when using the `socket` module

The error is also caused when sending data to a socket with the socket module.

main.py

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import socket

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(('example.com', 80))

# ⛔️ TypeError: a bytes-like object is required, not 'str'
s.send('GET https://example.com/example.txt HTTP/1.0\n\n')

while True:
    data = s.recv(1024)

    if not data:
        break
    print(data)

s.close()

One way to solve the error is to encode the str to a bytes object by using the encode() method.

You should also make sure to use the sendall() method instead of send(), because sendall() continues to send data from bytes until either all data has been sent or an error occurs.

main.py

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import socket

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(('example.com', 80))

# ✅ Call .encode('utf-8') on the string 👇️
s.sendall(
  'GET https://example.com/example.txt HTTP/1.0\n\n'.encode('utf-8')
)

while True:
    data = s.recv(1024)

    if not data:
        break
    print(data)

s.close()

We used the encode method to encode the string into bytes, which solves the error.

If you have a string literal, you can simply prefix it with b which achieves the same result.

main.py

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import socket

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(('example.com', 80))

# ✅ Prefix string literal with b''
s.sendall(b'GET https://example.com/example.txt HTTP/1.0\n\n')

while True:
    data = s.recv(1024)

    if not data:
        break
    print(data)

s.close()

Note that this approach can only be used with string literals. If the string is stored in a variable, use the .encode('utf-8') method instead.

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

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# (CSV) TypeError: a bytes-like object is required, not 'str'

To solve the Python CSV "TypeError: a bytes-like object is required, not 'str'", make sure to open the CSV file in w mode and not wb and use the io.StringIO class instead of io.BytesIO if working with streams.

csv bytes like object is required not str

Here is an example of how the error occurs.

main.py

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import csv


# 👇️ Note: file is open in wb mode
with open('example.csv', 'wb') as csvfile:
    csv_writer = csv.writer(csvfile, delimiter=',',
                            quoting=csv.QUOTE_MINIMAL)
    # ⛔️ TypeError: a bytes-like object is required, not 'str'
    csv_writer.writerow(['Alice', 'Bob', 'Carl'])

We opened the file in wb (binary) mode rather than w (text) mode which caused the error.

# Use the `w` mode when writing to a CSV file

To solve the error, use the w mode when writing to a CSV file.

main.py

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import csv

# ✅ Make sure to set the mode to `w` and set newline kwarg
with open('example.csv', 'w', newline='') as csvfile:
    csv_writer = csv.writer(csvfile, delimiter=',',
                            quoting=csv.QUOTE_MINIMAL)
    csv_writer.writerow(['Alice', 'Bob', 'Carl'])

We set the mode to w (text) and set the newline keyword argument to an empty string, which is mandatory when working with CSV files in Python 3.

If newline='' is not specified, newlines embedded inside quoted fields are not interpreted correctly.

For example, on platforms that use \r\n line endings on write, an extra \r will be added unless newline='' is specified.

If you are writing to an io.BytesIO object, use the io.StringIO class instead as the CSV writer only handles strings.

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# (JSON) TypeError: a bytes-like object is required, not 'str'

To solve the Python JSON "TypeError: a bytes-like object is required, not 'str'", make sure to open the JSON file in w mode and not wb mode when writing strings to a file.

json bytes like object is required not str

Here is an example of how the error occurs.

main.py

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import json

my_json = json.dumps({'name': 'Alice', 'age': 30})

file_name = 'example.json'

# 👇️ Opened the file in wb mode
with open(file_name, 'wb') as f:
    # ⛔️ TypeError: a bytes-like object is required, not 'str'
    f.write(my_json)

We opened the file in wb (binary) mode rather than w (text) mode which caused the error.

# Use the `w` mode when writing to a JSON file

To solve the error, use the w mode when writing to a JSON file.

main.py

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import json

my_json = json.dumps({'name': 'Alice', 'age': 30})

file_name = 'example.json'

# ✅ opened file in w mode and set encoding to utf-8
with open(file_name, 'w', encoding='utf-8') as f:
    f.write(my_json)

We opened the JSON file in w (text) mode.

When a file is opened in text mode, we read and write strings from and to the file.

Those strings are encoded using a specific encoding (utf-8 in the example).

Note that if you don't explicitly set the encoding keyword argument, the default is platform-dependent.

If you want to both read from and write to the file, use the r+ mode when opening it.

If you append a b to the mode (like in the first code snippet), the file is opened in binary mode.

Note that you cannot specify encoding when opening a file in binary mode.

When a file is opened in binary mode, data is read and written as bytes objects.

This means that you could encode your JSON string to a bytes object using the encode() method if you have the wb mode set.

main.py

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import json

my_json = json.dumps({'name': 'Alice', 'age': 30})

file_name = 'example.json'

with open(file_name, 'wb') as f:
    f.write(my_json.encode('utf-8'))

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

However, it is much simpler to open the JSON file in w (or another text) mode, so you can write strings directly.

# TypeError: a bytes-like object is required, not _io.BytesIO

To solve the Python "TypeError: a bytes-like object is required, not _io.BytesIO", call the read() method on the _io.BytesIO object, e.g. b.read().

The read method reads the bytes from the object and returns them.

typeerror typeerror bytes like object is required not str

Here is an example of how the error occurs.

main.py

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import io

b = io.BytesIO(b"abcd")

print(type(b)) # <class '_io.BytesIO'>

with open('example.zip', 'wb') as f:
    # ⛔️ TypeError: a bytes-like object is required, not '_io.BytesIO'
    f.write(b)

We tried using an _io.BytesIO object where a bytes object is expected.

To solve the error, call the read() method on the _io.BytesIO object.

main.py

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import io

b = io.BytesIO(b"abcd")

print(type(b))  # <class '_io.BytesIO'>

with open('example.zip', 'wb') as f:
    # 👇️ Change the stream position to the start
    b.seek(0)

    # 👇️ Read the bytes from the object
    f.write(b.read())

We used the seek() method to change the stream position to an offset of 0 (to the beginning).

This means that we will start reading the stream from the start.

The read() method can be used to read the bytes from an object and return them.

The method takes an optional size argument if you want to specify up to how many bytes to return.

If the argument is not provided, all bytes until the end of the file are returned.

Calling the seek() method with a position of 0 is important because if you use the `read` method somewhere else in your code, you would change the offset.

Here is an example that demonstrates this - once we call the read() method, the stream is positioned at the end, so it doesn't return anything.

main.py

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import io

b = io.BytesIO(b"abcd")

with open('example.zip', 'wb') as f:
    # 👇️ Change the stream position to the start
    b.seek(0)

    print(b.read())  # 👉️ b'abcd'
    print(b.read())  # 👉️ b''

You can use the seek(0) method to reset the stream position.

main.py

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import io

b = io.BytesIO(b"abcd")

with open('example.zip', 'wb') as f:
    # 👇️ Change the stream position to the start
    b.seek(0)

    print(b.read())  # 👉️ b'abcd'

    # 👇️ Change the stream position to the start
    b.seek(0)

    print(b.read())  # 👉️ b'abcd'

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

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