Lessons · Regex · \d is more digits than you think

More digits than you think

\d means any Unicode decimal digit, which includes scripts other than this one. [0-9] means exactly those ten characters.

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What it is for

If the value is going to int(), \d is fine, because Python parses those too. If it is going into a fixed-width field or a bank format, it is not.

Ask what the field is FOR. 'A digit' is \d. 'One of these ten characters' is [0-9], and it cannot widen underneath you later.

re.match(r'\d+', '\u0661\u0662\u0663').group()

Arabic-Indic digits are digits.

re.match(r'[0-9]+', '\u0661\u0662\u0663')

The explicit range is not fooled.

int('\u0661\u0662\u0663')

And Python really does parse them, which is why \d is not simply wrong.

Match only the characters 0 to 9.

The two agree on every English digit, so a test suite written in English never tells them apart.

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