TypeError: unsupported operand type(s) for -: str and str

TypeError: unsupported operand type(s) for -: str and str #

The Python "TypeError: unsupported operand type(s) for -: 'str' and 'str'" occurs when we try to use the subtraction - operator with two strings. To solve the error, convert the strings to int or float values, e.g. int(my_str_1) - int(my_str_2).

Here is an example of how the error occurs.

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my_str_1 = '50'

my_str_2 = '20'

# ⛔️ TypeError: unsupported operand type(s) for -: 'str' and 'str'
result = my_str_1 - my_str_2

We are trying to use the subtraction operator with two values of type string.

To solve the error, we have to convert the strings to numbers (e.g. integers or floats).

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my_str_1 = '50'

my_str_2 = '20'

result = int(my_str_1) - int(my_str_2)

print(result) # 👉️ 30

We used the int() class to convert the strings to integers before using the subtraction operator.

If you have floats wrapped in strings, use the float() class instead.

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my_str_1 = '50'

my_str_2 = '20'

result = float(my_str_1) - float(my_str_2)

print(result)  # 👉️ 30.0

If you have a string that may also contain characters but you only need to extract an integer, use the filter() function to filter out all non-digits.

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my_str_1 = 'a 5 b 0'

my_num_1 = int(''.join(filter(str.isdigit, my_str_1)))
print(my_num_1)  # 👉️ 50

my_str_2 = '20'

result = my_num_1 - int(my_str_2)

print(result)  # 👉️ 30

The filter function takes a function and an iterable as arguments and constructs an iterator from the elements of the iterable for which the function returns a truthy value.

The str.isdigit method returns True if all characters in the string are digits and there is at least 1 character, otherwise False is returned.

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

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my_str_1 = '50'
print(type(my_str_1))  # 👉️ <class 'str'>
print(isinstance(my_str_1, str))  # 👉️ True

my_int_1 = 20
print(type(my_int_1))  # 👉️ <class 'int'>
print(isinstance(my_int_1, int))  # 👉️ 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.