How to Fix TypeError: Non-Empty Format String Passed to Object.__format__ in Python

The format() method in python lets you substitute variables and performs data formatting. This method is not designed to deal with any inputs other than the following:

• String denoted as s
• Decimal denoted as d
• Float denoted as f
• Character denoted as c
• Octal denoted as o
• Hexadecimal denoted as x
• Binary denoted as b
• Exponential is denoted as e

If any other data type accesses the method, the interpreter raises the below error:

TypeError: non-empty format string passed to object.__format__

Causes and Solutions to TypeError: Non-Empty Format String Passed to Object.__format__ in Python

Suppose we try to invoke the format() method on a data type that does not have this method, for example, the byte data type. The interpreter will raise an error because the byte type object has no format() method.

In the following code, we have intentionally invoked the format() method with the byte data type.

Example Code:

# Python 3.x
"{:10}".format(b"delftstack")

Output:

#Python 3.x
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-12-1909c614b7f5> in <module>()
----> 1 '{:10}'.format(b'delftstack')

TypeError: unsupported format string passed to bytes.__format__

The solution to this error is explicitly converting the data type from byte to string. We will use the !s symbol for conversion.

Example Code:

# Python 3.x
s = "{!s:10s}".format(b"delftstack")
print(s)

Output:

#Python 3.x
b'delftstack'

The TypeError: non-empty format string passed to object.__format__ is also raised when we try to format None.

Example Code:

# Python 3.x
"{:.0f}".format(None)

Output:

#Python 3.x
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-4-89103a1332e2> in <module>()
----> 1 '{:.0f}'.format(None)

TypeError: unsupported format string passed to NoneType.__format__

The solution is to pass a valid data type instead of None.

Example Code:

# Python 3.x
s = "{!s:10s}".format(b"delftstack")
print(s)

Output:

#Python 3.x
b'delftstack'