How to Check If a Python String Can Convert to an Integer

The most reliable way to check whether a Python string can convert to an integer is to call int() inside a try and except block.

def can_convert_to_int(value: str) -> bool:
    try:
        int(value)
    except (TypeError, ValueError):
        return False
    return True


print(can_convert_to_int("42"))    # True
print(can_convert_to_int("-42"))   # True
print(can_convert_to_int("3.14"))  # False

This tests the conversion you intend to perform, so it handles signs and whitespace correctly.

Convert and validate at the same time

If you need the converted value, avoid validating and then converting in two separate steps:

raw_value = " -42 "

try:
    number = int(raw_value)
except ValueError:
    print("Enter a whole number")
else:
    print(number)  # -42

The else block runs only when conversion succeeds.

Why str.isdigit() is not always enough

isdigit() is convenient when a value must contain only digit characters:

"42".isdigit()    # True
"-42".isdigit()   # False
" 42 ".isdigit() # False

It rejects a leading sign and surrounding whitespace, even though int() accepts those strings. Use isdigit() for deliberately strict digit-only input and int() when the question is whether Python can convert the value.

Check without using exceptions

For ASCII integers with an optional sign, remove whitespace and inspect the remaining characters:

def is_ascii_integer(value: str) -> bool:
    value = value.strip()
    if value.startswith(("+", "-")):
        value = value[1:]
    return bool(value) and value.isascii() and value.isdigit()

The bool(value) check prevents an empty string or a sign by itself from being accepted.

Common edge cases

Input	Conversion succeeds?	Notes
"42"	Yes	Ordinary integer
"-42"	Yes	Negative integer
"+42"	Yes	Explicit positive sign
" 42 "	Yes	Whitespace is ignored
"3.0"	No	Decimal string
"1,000"	No	Separators need separate handling
""	No	Empty string
None	No	Raises TypeError

Do not convert a decimal string with int(float(value)) unless truncating the decimal portion is explicitly intended.

Validate values from forms and CSV files

Conversion and business validation are separate steps:

def parse_quantity(raw_value: str) -> int:
    try:
        quantity = int(raw_value)
    except (TypeError, ValueError) as error:
        raise ValueError("Quantity must be a whole number") from error

    if quantity < 0:
        raise ValueError("Quantity cannot be negative")

    return quantity

Quick reference

• Use int() with try/except for the most accurate test.
• Catch ValueError, and also TypeError if None is possible.
• Use isdigit() only when signs and whitespace must be rejected.
• Convert once and retain the result rather than checking and converting twice.

Next, see how to convert every item in a list to integers.