Extract digits from string

Return all digit characters from a string as a single string, preserving order.

strings digits parsing filter

Write a function `extract_digits(s: str) -> str` that takes a single string `s` and returns a new string containing only the digit characters (0-9) from `s`, in the same order they appear. Non-digit characters are ignored. If there are no digits, return an empty string.

- The input string may contain letters, spaces, punctuation, and digits.
- The function should handle empty strings correctly.
- Do not use any external libraries.

Constraints

- `s` is a string with length 0 to 10,000.
- The function should return a string consisting only of digit characters.

Example

>>> extract_digits("Order 1234: 5 apples")
'12345'
>>> extract_digits("abc!?")
''
>>> extract_digits("")
''
>>> extract_digits("A1B2C3")
'123'

6 points ~8 min

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Hints

Iterate over each character in the string and check if it is a digit.

Use `str.isdigit()` to test each character.

Collect the digits into a list and join them at the end.

An empty string input should return an empty string.

Test Results

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