Python Check If Number is an Integer

Source: Dev.to

def is_int(x: int | float | str | None):
    """
    Return True if *x* represents an integer value, otherwise False.

    Handles:
    - int, float, and numeric strings (e.g., "12", "12.0")
    - None or non‑numeric strings gracefully return False
    """
    try:
        return float(x).is_integer()
    except (TypeError, ValueError):
        return False

How it works

• float(x) attempts to convert the input to a floating‑point number.
• is_integer() checks whether the resulting float has no fractional part.
• If the conversion fails (e.g., x is None or a non‑numeric string), a TypeError or ValueError is caught and the function returns False.

Example usage (test cases)

# Positive cases – should return True
a1 = 12.0
a2 = "12.0"
a3 = "012.0"

b1 = 12
b2 = "12"
b3 = "012"

# Negative cases – should return False
c1 = 12.34
c2 = "12.34"
c3 = "012.34"

d1 = None
d2 = "12X100ML"
d3 = "12.x"

print(is_int(a1))  # True
print(is_int(a2))  # True
print(is_int(a3))  # True

print(is_int(b1))  # True
print(is_int(b2))  # True
print(is_int(b3))  # True

print(is_int(c1))  # False
print(is_int(c2))  # False
print(is_int(c3))  # False

print(is_int(d1))  # False
print(is_int(d2))  # False
print(is_int(d3))  # False

Why isinstance(x, int) isn’t enough

• String numbers: "12" or "12.0" are not int instances.
• Floats that are mathematically integers: 12.0 is a float but represents an integer value.
• Invalid inputs: Non‑numeric strings like "abc" or "12.x" should return False without raising an exception.

Alternative (more verbose) implementation

def is_int(x: int | float | str | None):
    if isinstance(x, str):
        try:
            x = float(x)
        except (TypeError, ValueError):
            return False

    if isinstance(x, int):
        return True

    if isinstance(x, float):
        return x.is_integer()

    return False

Regex approach

A regular‑expression solution is possible but adds unnecessary complexity. The built‑in conversion shown above is concise and reliable. (For a regex version, see my other post.)