How to Convert a String to an Integer in Python (With Examples)

Working with numbers stored as strings is a common task in Python programming. Whether you’re parsing user input, reading data from a file, or working with APIs, you’ll often need to transform numeric strings into integers for calculations. Luckily, Python provides a simple yet powerful way to handle this using the built-in int() function.

In this guide, we’ll walk through the different methods to safely and efficiently convert strings to integers in Python, including handling special bases (binary, hexadecimal), invalid inputs, and float-like strings. We’ll also cover best practices to avoid common pitfalls.

Method 1: Convert a Decimal String to an Integer

The most basic case is when your string represents a decimal number.

s = "42"
n = int(s)
print(n * 2)  # Output: 84

✅ Tip: The int() function ignores leading/trailing spaces and supports signs like +17 or -3.

Method 2: Convert Strings in Other Bases (Binary, Hex, Octal)

If your string represents a number in another base, simply pass the base as the second argument.

# Binary
b = "1010"
n = int(b, 2)   # Output: 10

# Hexadecimal
h = "1A"
m = int(h, 16)  # Output: 26

📌 Python supports any base from 2 to 36, making it versatile for different numeral systems.

Method 3: Handle Invalid Input Safely

When converting user input, mistakes happen. Protect your code with try/except blocks.

s = "abc"
try:
    n = int(s)
    print(n)
except ValueError:
    print("Invalid input: cannot convert to integer")

You can also pre-validate with str.isdigit() if you only expect positive integers:

s = "12345"
if s.isdigit():
    print(int(s))
else:
    print("Not a pure digit string")

⚠️ Note: isdigit() does not accept negative signs (-5) or decimals (12.3). Use try/except for those cases.

Method 4: Convert Float-Like Strings to Int

Sometimes, numeric strings contain decimals. In that case, convert to a float first, then cast to an int.

s = "88.8"
n = int(float(s))  # Output: 88 (fractional part truncated)

👉 If you prefer rounding instead of truncation:

s = "88.8"
n = round(float(s))  # Output: 89

Method 5: Convert a List of Strings to Integers

For lists of numbers stored as strings, use list comprehension or map():

xs = ["1", "2", "3"]

# Using map
nums = list(map(int, xs))  # [1, 2, 3]

# Using list comprehension
nums = [int(x) for x in xs]

If some items may be invalid, wrap the logic in a custom function with try/except.

Common Pitfalls to Avoid

• ❌ Converting non-numeric strings like "hello" → raises ValueError.
• ❌ Parsing "12.5" directly with int() → fails (must convert to float first).
• ❌ Forgetting the correct base → "1010" without base=2 parses as decimal 1010, not binary.

Final Thoughts

Converting strings to integers in Python is straightforward with the int() function, but knowing how to handle different formats and errors will make your programs far more reliable. Whether you’re working with binary values, validating user input, or cleaning messy data, these techniques will help you write clean, efficient, and error-proof code.

Mastering these small details is what separates good Python code from great Python code.