python 31 lines · 8 steps

Parsing duration strings like 1h30m in Python

A regex scanner turns compact duration strings into a total number of seconds while rejecting malformed input.

Explained by highlit
Intermediate regex parsing validation tokenizing
1import re
2 
3_UNIT_SECONDS = {
4 "w": 604800,
5 "d": 86400,
6 "h": 3600,
7 "m": 60,
8 "s": 1,
9}
10 
11_TOKEN = re.compile(r"(\d+)([wdhms])")
12 
13 
14def parse_duration(value: str) -> int:
15 text = value.strip().lower()
16 if not text:
17 raise ValueError("empty duration string")
18 
19 pos = 0
20 total = 0
21 for match in _TOKEN.finditer(text):
22 if match.start() != pos:
23 raise ValueError(f"unexpected token near {text[pos:]!r}")
24 amount, unit = match.groups()
25 total += int(amount) * _UNIT_SECONDS[unit]
26 pos = match.end()
27 
28 if pos != len(text):
29 raise ValueError(f"invalid duration: {value!r}")
30 
31 return total
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1A lookup table maps units to a common base so each token contributes cleanly to one total.
  2. 2Tracking the match position lets a regex scanner detect gaps and reject unexpected characters.
  3. 3Validating that the scan reached the end of the string catches trailing junk the pattern skipped.

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