Not all arguments converted during string formatting (Python)

# Not all arguments converted during string formatting (Python)

The Python "TypeError: not all arguments converted during string formatting" occurs when we use incorrect syntax to format a string or use the % operator with a string and a number.

To solve the error, call the format() method on the string and provide values for all placeholders.

Here is an example of how to use the str.format() method.

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# ✅ Using str.format() correctly

first = 'James'
last = 'Doe'

result = "His name is {0} {1}".format(first, last)

print(result)  # 👉️ "His name is James Doe"

The str.format() method performs string formatting operations.

The string the method is called on can contain replacement fields specified using curly braces {}.

# Using the modulo operator with a string and an integer

The error also occurs when you try to use the % (modulo) operator with a string and an integer.

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my_str = '99'

result = my_str % 5

# ⛔️ TypeError: not all arguments converted during string formatting
print(result)

To solve the error, use the int() class to convert the string to an integer.

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my_str = '99'

# ✅ convert to int
result = int(my_str) % 5

print(result)  # 👉️ 4

We used the int() class to convert the string to an integer to be able to use the modulo % operator.

Once the values on both sides of the % (modulo) operator are integers, the error will be resolved.

# The input() function always returns a string

Note that the input() function always returns a string, even if the user enters an integer.

If you take input from the user, make sure to use the int() class to convert the value to an integer.

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# ✅ Convert a value to an integer with int()
num = int(input('Enter your fav number: '))

print(num) # 👉️ 10
print(type(num))  # 👉️ <class 'int'>

# Using the str.format() method correctly

If you get the error while formatting a string, make sure that each replacement field contains either the numeric index of a positional argument or the name of a keyword argument.

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first = 'James'

last = 'Doe'

result = "His name is {f} {l}".format(f=first, l=last)

print(result)  # 👉️ "His name is James Doe"

The example uses keyword arguments instead of positional ones.

If you decide to use positional arguments with numeric indices, make sure to start from 0, e.g. {0} as indices are zero-based in Python.

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first = 'James'
last = 'Doe'

result = "His name is {0} {1}".format(first, last)

print(result)  # 👉️ "His name is James Doe"

# Using a formatted string literal to solve the error

Alternatively, you can use a formatted string literal to concatenate strings.

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first = 'Bobby'

last = 'Hadz'

result = f'His name is {first} {last}'

print(result)  # 👉️ "His name is Bobby Hadz"

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

This should be your preferred approach as formatted string literals are a more recent addition to Python and offer a much easier-to-read syntax.

Formatted string literals also take care of converting the value to a string automatically.

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name = 'Bobby'

age = 30

result = f'{name} is {age} years old.'

print(result)  # 👉️ "Bobby is 30 years old."

We didn't have to convert the integer to a string which would have been the case had we used the addition (+) operator.

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name = 'Bobby'

age = 30

result = name + ' is ' + str(age) + ' years old.'

print(result)  # 👉️ "Bobby is 30 years old."

# Checking what type the variable stores

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

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my_str = '99'
print(type(my_str))  # 👉️ <class 'str'>
print(isinstance(my_str, str))  # 👉️ True


my_num = 5
print(type(my_num))  # 👉️ <class 'int'>
print(isinstance(my_num, 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.

I've also written an article on how to use f-strings for conditional formatting.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• Split a String and remove the Whitespace in Python
• Split a String and get First or Last element in Python
• Split a String into a List of Integers in Python
• Split a String into multiple Variables in Python
• Split a String into Text and Number in Python