ValueError

ValueError is raised when a function receives an argument of the right type but an inappropriate value. For example, int('abc') raises ValueError because 'abc' is a string (correct type) but not a valid integer representation.

Common causes

• Converting invalid strings to numbers: int("abc")
• Unpacking wrong number of values
• Passing out-of-range values to math functions
• Invalid arguments to list.remove() for missing elements
• Incorrect date/time format strings

How to fix it

• Validate input before conversion
• Use try/except ValueError to handle conversion failures
• Check value ranges before passing to functions
• Use "if item in list" before list.remove(item)
• Parse dates with error handling using strptime

Example

# Error example
number = int("abc")
# ValueError: invalid literal for int() with base 10: 'abc'

a, b = [1, 2, 3]
# ValueError: too many values to unpack (expected 2)

# Fix with try/except
def safe_int(value, default=0):
    try:
        return int(value)
    except ValueError:
        return default

safe_int("abc")  # 0

# Fix unpacking
a, b, *rest = [1, 2, 3]  # a=1, b=2, rest=[3]

# Validate before removing
items = [1, 2, 3]
if 4 in items:
    items.remove(4)

Related errors