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

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

The Python "TypeError: can only concatenate list (not "str") to list" occurs when we try to concatenate a list and a string. To solve the error, use the append() method to add an item to the list, e.g. my_list.append('my item').

Here is an example of how the error occurs.

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my_list = ['apple', 'banana']

my_str = 'melon'

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

We tried to use the addition (+) operator to add an item to a list which caused the error.

You can use the append() method to add an item to a list.

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my_list = ['apple', 'banana']

my_str = 'melon'

my_list.append(my_str)

print(my_list)  # 👉️ ['apple', 'banana', 'melon']

The list.append() method adds an item to the end of the list.

The method returns None as it mutates the original list.

Alternatively, you can wrap the string in a list if you'd prefer to use the addition (+) operator.

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my_list = ['apple', 'banana']

my_str = 'melon'

result = my_list + [my_str]

print(result)  # 👉️ ['apple', 'banana', 'melon']

However, using the append() method is much more common.

Conversely, if you need to remove an item from a list, use the remove() method.

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my_list = ['apple', 'banana']

my_str = 'banana'

my_list.remove(my_str)

print(my_list)  # 👉️ ['apple']

The list.remove() method removes the first item from the list whose value is equal to the passed in argument.

The method raises a ValueError if there is no such item.

The remove() method mutates the original list and returns None.

If you meant to print the contents of the list, use a formatted string literal.

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my_list = ['apple', 'banana']

my_str = 'are fruits'

result = f'{my_list} {my_str}'

print(result)  # 👉️ ['apple', 'banana'] are fruits

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

If you meant to concatenate an item from the list with a string, access the item at the specific index using square brackets.

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my_list = ['apple', 'banana']

my_str = ' is my fav fruit'

result = my_list[0] + my_str

print(result)  # 👉️ 'apple is my fav fruit'

We accessed the list element at index 0, which is a string, so we were able to concatenate the two strings.

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

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my_list = ['apple', 'banana']
print(type(my_list))  # 👉️ <class 'list'>
print(isinstance(my_list, list))  # 👉️ True


my_str = 'are fruits'
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 only concatenate list (not "str") to list" occurs when we try to concatenate a list and a string. To solve the error, use the append() method to add an item to the list, e.g. my_list.append('my item').