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

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

The Python "TypeError: can only concatenate str (not "set") to str" occurs when we try to concatenate a string and a set. To solve the error, use a formatted string literal, or use the add() method to add an item to the set.

Here is an example of how the error occurs.

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my_str = 'fruits: '

my_set = {'apple', 'banana', 'kiwi'}

# ⛔️ TypeError: can only concatenate str (not "set") to str
print(my_str + my_set)

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

If you only need to print the contents of the set, use a comma between the string and the set.

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my_str = 'fruits: '

my_set = {'apple', 'banana', 'kiwi'}

# 👇️ fruits:  {'apple', 'kiwi', 'banana'}
print(my_str, my_set)

Alternatively, you can use a formatted string literal.

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my_str = 'fruits:'

my_set = {'apple', 'banana', 'kiwi'}

result = f'{my_str} {my_set}'
print(result)  # 👉️ fruits: {'kiwi', 'apple', 'banana'}

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

If you need to add an item to the set, use the add() method.

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my_str = 'fruits: '

my_set = {'apple', 'banana', 'kiwi'}

my_set.add('melon')

# 👇️ {'kiwi', 'banana', 'apple', 'melon'}
print(my_set)

The set.add method adds the provided element to the set.

You can also pass the set to the str() class to convert it to a string before concatenating the two strings.

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my_str = 'fruits: '

my_set = {'apple', 'banana', 'kiwi'}

result = my_str + str(my_set)

# 👇️ fruits: {'kiwi', 'apple', 'banana'}
print(result)

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

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


my_set = {'apple', 'banana', 'kiwi'}
print(type(my_set))  # 👉️ <class 'set'>
print(isinstance(my_set, set))  # 👉️ 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 str (not "set") to str" occurs when we try to concatenate a string and a set. To solve the error, use a formatted string literal, or use the add() method to add an item to the set.