Solution preview: convert a numeric string with int(). For non‑decimal inputs (binary, hex) pass a base. Add error handling or pre‑validation to deal with invalid input.

Method 1: Convert a decimal numeric string with int()

Step 1: Store or read the numeric string.

s = "42"

Step 2: Convert the string to an integer.

n = int(s)

Step 3: Use the integer in calculations or print it.

print(n * 2)  # 84

Tip: int() ignores leading/trailing whitespace and supports optional signs like "+17" or " -3 ".

Method 2: Parse strings in other bases (binary, hex, octal)

Step 1: Identify the base of your string (2 for binary, 8 for octal, 16 for hex).

Step 2: Pass the base as the second argument to int().

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

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

Note: You can use any base between 2 and 36.

Method 3: Handle invalid input safely (try/except or pre-check)

Step 1: Wrap the conversion in a try/except block to catch bad input.

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

Step 2: Optionally pre‑validate with str.isdigit() for digit‑only inputs.

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

Check: str.isdigit() does not accept signs ("-5") or decimals ("12.3"). Use the try/except path for those cases.

Method 4: Convert float-like strings to int

Step 1: Convert the string to a float, then to an int.

s = "88.8"
n = int(float(s))  # 88 (truncates toward zero)

Note: This truncates the fractional part. If you need rounding, convert to float and apply round() before int().

Method 5: Convert a list of numeric strings

Step 1: Map each element through int to build a new list.

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

Step 2: Alternatively, use a list comprehension.

nums = [int(x) for x in xs]

Tip: If items might be invalid, wrap the conversion in a function that uses try/except and apply it with map or a comprehension.

Common pitfalls

  • Passing non-numeric text (for example, "hello") raises ValueError. Use try/except to keep your program running.
  • Parsing a float string (for example, "12.5") with int() fails; convert to float first if truncation is acceptable.
  • Parsing base-specific strings without the correct base gives incorrect results or errors. Always pass the base when the string isn’t decimal.

With int() for direct parsing, a base argument for non-decimal strings, and simple validation, you can convert inputs confidently and keep your code robust.