Number Parsing in Python

Our first example demonstrates parsing numbers from strings, which is a common task in many programs. Here’s how to do it in Python:

# Python's built-in functions handle number parsing

def main():
    # Parse a float
    f = float("1.234")
    print(f)

    # Parse an integer
    i = int("123")
    print(i)

    # Parse a hexadecimal number
    d = int("0x1c8", 16)
    print(d)

    # Parse an unsigned integer (same as int in Python)
    u = int("789")
    print(u)

    # Parse a base-10 integer (same as int)
    k = int("135")
    print(k)

    # Parsing functions raise an exception on bad input
    try:
        int("wat")
    except ValueError as e:
        print(e)

if __name__ == "__main__":
    main()

Let’s break down the key points:

1. Python’s built-in float() function is used to parse floating-point numbers from strings.

2. The int() function is used to parse integers. It can handle different bases:

   • By default, it parses base-10 integers.
   • To parse hexadecimal numbers, we pass the base as the second argument: int("0x1c8", 16).

3. Python doesn’t have separate types for signed and unsigned integers, so we use int() for both cases.

4. There’s no direct equivalent to Go’s Atoi() function in Python, but int() serves the same purpose for base-10 integers.

5. When parsing fails, Python raises a ValueError exception, which we can catch and handle.

Here’s what you’d see if you run this program:

$ python number_parsing.py
1.234
123
456
789
135
invalid literal for int() with base 10: 'wat'

This example demonstrates how Python handles number parsing, which is generally simpler and more straightforward compared to some other languages, as it relies on built-in functions and doesn’t require importing additional modules for basic parsing tasks.

Next, we’ll look at another common parsing task: URLs.