TypeError: expected string or bytes-like object in Python

# TypeError: expected string or bytes-like object in Python

The Python "TypeError: expected string or bytes-like object" occurs when you pass a non-string argument to a function that expects a string.

To solve the error, make sure to call the function with a string argument instead.

Here is an example of how the error occurs.

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import re

my_int = 100

# ⛔️ TypeError: expected string or bytes-like object
result = re.sub(r'[0-9]', '_', my_int) # 👈️ Third arg must be str

We passed an integer as the third argument to the re.sub method, but the method expects a string argument.

The re.sub() method takes 3 arguments:

1. A pattern to match in a string.
2. The replacement string for the matches.
3. The string in which to match the pattern.

# Convert the value to a string to solve the error

One way to solve the error is to use the str() class to convert the value to a string.

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import re

my_int = 100

# ✅ convert to str
result = re.sub(r'[0-9]', '_', str(my_int))

print(result) # 👉️ '___'

We used the str() class to convert the integer to a string when calling re.sub().

You might also be iterating over a sequence and calling the re.sub() method with each item.

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import re

my_list = [0, 10, 100]

new_list = []

for item in my_list:
    result = re.sub(r'[0-9]', '_', str(item))
    print(result)

    new_list.append(result)

print(new_list)  # 👉️ ['_', '__', '___']

We used a for loop to iterate over the list.

On each iteration, we pass the current item to the str() class before using re.sub().

# Providing a fallback value for None values

If your sequence stores None values, provide an empty string as a fallback.

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import re

my_value = None

result = re.sub(r'[0-9]', '_', my_value or '')

print(repr(result))  # 👉️ ''

The expression None or '' evaluates to an empty string which helps us avoid the error.

The re.sub() method returns a new string that is obtained by replacing the occurrences of the pattern with the provided replacement.

Here is an example of how to solve the error when working with lists.

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import re
from ast import literal_eval


my_list = [5, 'a', 0, 'b', 1, 'c', 2, 6]

# ✅ remove letters from a list
my_str = re.sub(r'[a-zA-Z]+', '', str(my_list))
print(my_str)  # 👉️ [5, '', 0, '', 1, '', 2, 6]

# ✅ remove empty strings from a string
new_str = my_str.replace("''", '')
print(new_str)  # 👉️ [5, , 0, , 1, , 2, 6]

# ✅ remove double commas from a string
new_str = new_str.replace(", ,", ',')
print(new_str)  # 👉️ [5, 0, 1, 2, 6]

# ✅ convert the string representation of list to list
my_list = literal_eval(new_str)
print(my_list)  # 👉️ [5, 0, 1, 2, 6]
print(type(my_list))  # 👉️ <class 'list'>

1. We first remove all letters from the list, converting the list to a string.
2. Then we remove all empty strings from the string and replace double commas with a single comma.
3. The last step is to use the literal_eval() method to convert the string to a list.

You might also get the error when using the re.findall() method.

# Encountering the error when using re.findall()

Here is an example of how the error occurs when using re.findall().

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import re

my_int = 100

# ⛔️ TypeError: expected string or bytes-like object, got 'int'
result = re.findall(r'[0-9]',  my_int)

To solve the error, convert the second argument in the call to findall() to a string.

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import re

my_int = 100

result = re.findall(r'[0-9]',  str(my_int))

print(result)  # 👉️ ['1', '0', '0']

We used the str() class to convert a value to a string before calling re.findall().

Here is another example of how the error occurs when using the re.findall() method.

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import re

with open('example.txt', 'r', encoding='utf-8') as f:
    lines = f.readlines() # 👈️ this is a list

    # ⛔️ TypeError: expected string or bytes-like object
    m = re.findall(r'\w+th', lines) # 👈️ passing list instead of str

We passed a list to the re.findall method, but the method takes a string argument.

To solve the error, call the read() method on the file object to get a string of the file's contents and pass the string to the findall method.

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import re

with open('example.txt', 'r', encoding='utf-8') as f:
    my_str = f.read()
    print(type(my_str))  # 👉️ <class 'str'>

    m = re.findall(r'\w+th', my_str)
    print(m)  # 👉️ ['fourth', 'fifth']

The example assumes that you have a file named example.txt with the following contents:

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first
second
third
fourth
fifth

All we had to do was make sure we passed a string as the second argument to the re.findall method.

The re.findall method takes a pattern and a string as arguments and returns a list of strings containing all non-overlapping matches of the pattern in the string.

# Solve the error when reading from a JSON file

If you got the error while trying to read a JSON file, use the json.load() method.

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import json

file_name = 'example.json'

with open(file_name, 'r', encoding='utf-8') as f:
    my_data = json.load(f) # ✅ call json.load() with file obj

    print(my_data)  # 👉️ {'name': 'Alice', 'age': 30}
    print(my_data['name'])  # 👉️ 'Alice'
    print(type(my_data))  # 👉️ <class 'dict'>

The code sample above assumes that you have an example.json file in the same directory.

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{"name": "Alice", "age": 30}

The json.load() method is used to deserialize a file to a Python object, whereas the json.loads() method is used to deserialize a JSON string to a Python object.

The json.load() method expects a text file or a binary file containing a JSON document that implements a .read() method.

If the error persists, use your IDE to check the type of the method's parameters.

# Checking what type a variable stores

If you aren't sure what type of object 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_dict = {'name': 'Alice', 'age': 30}
print(type(my_dict))  # 👉️ <class 'dict'>
print(isinstance(my_dict, dict))  # 👉️ 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.