How to Solve the ValueError: Zero Length Field Name in Format Error in Python

String formatting is a very common practice in Python to alter the representation of the string so that we can view it in our desired format. Python provides a variety of methods for string formatting; some are the format() function, f-strings, and more.

The format() function takes a string and converts it to our desired format. It is very simple to use and works with Python 2 and Python 3.

The format() function can specify replacement fields in a string using the curly braces {}. We specify the values for this replacement field within the format() function.

This tutorial will discuss the ValueError: zero length field name in format error in Python.

Solve the ValueError: zero length field name in format Error in Python

This error is a ValueError, meaning an invalid value of the correct data type was specified in the function parameter. Think of it as providing -16 as the value in a square-root function.

Even though the value type is an int, it will provide a ValueError since it’s an invalid value.

Let us discuss a sample case of the ValueError: zero length field name in format error.

See the code below.

# python 2.x
x, y = 4, 5
print "X ({}) < B ({})".format(x, y)

Output:

ValueError: zero length field name in format

This error is encountered only in specific versions of Python. It is encountered in Python 2.6 or below or in Python 3.0 (not in 3.1 and above).

This error is not encountered in any other version of Python.

The compiler throws this error because, in these specified versions, we need to provide the positional argument specifier for the replacement fields. To fix this error, we would be required to add the indexes in the respective curly braces.

For example,

x, y = 4, 5
print("X ({0}) < B ({1})".format(x, y))

Output:

X (4) < B (5)

The above solution should fix the error.

The reason why other versions of Python (2.7 and above, excluding 3.0) do not encounter this error is that in these versions, the format() function can omit the positional argument specifiers, which means that {}{} will be understood as {0}{1} by default.