Python input exercise: accept an explicit integer grammar

Operation contract

The receipt wire field accepts one to eight ASCII decimal digits and a positive result. It rejects a leading plus sign, surrounding whitespace, zero and non-ASCII decimal glyphs. Python int accepts some forms that this wire format intentionally excludes; relying on conversion alone would implement a broader grammar than the API promises.

Failure and ownership boundary

The parser has a small input cap and separates textual shape from numeric positivity. Changing that grammar is an API change, not merely a display improvement. Python functions: define units, validate input and return a result and Python Decimal money: parse decimal text and choose rounding explicitly handle different input models; do not mix their accepted representations accidentally.

Working program

def wire_amount(text):
    if not 1 <= len(text) <= 8 or any(character not in "0123456789" for character in text):
        raise ValueError("ASCII digit field required")
    amount = int(text)
    if amount == 0:
        raise ValueError("positive amount required")
    return amount

print(wire_amount("125"))
for text in ["+125", " 125", "0", "１２５"]:
    try:
        wire_amount(text)
    except ValueError:
        print("field rejected")

Output

125
field rejected
field rejected
field rejected
field rejected

Costs and limits

The declared eight-character cap bounds parsing work and integer size. This grammar does not identify a currency, user or authorized receipt operation.

Common Mistakes

• Conversion accepts more than every narrow wire grammar.
• Validate textual shape and domain range separately.

Connected lessons

Python functions: define units, validate input and return a result, Python Decimal money: parse decimal text and choose rounding explicitly, Python JSON validation: reject duplicate members and non-integer amounts.

Apply this boundary

Django forms: ASCII wire fields and cleaned domain values.