# ERROR: Invalid requirement: 'package>=1.0,<2.0' (from line 1 of requirements.txt) - Expected end or semicolon

- **ID:** `python/pip-invalid-requirement-parse-error`
- **Domain:** python
- **Category:** config_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

The requirement string contains a comma-separated version specifier without proper spacing or a malformed operator, causing the parser to fail.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.9 | active | — | — |

## Workarounds

1. **** (95% success)
   ```
   Rewrite as 'package>=1.0, <2.0' (with space after comma) or 'package>=1.0,<2.0' (no space but valid)
   ```
2. **** (90% success)
   ```
   sed -i 's/>=1.0,<2.0/>=1.0,<2.0/' requirements.txt && pip install -r requirements.txt
   ```
3. **** (85% success)
   ```
   Create constraints.txt with 'package>=1.0,<2.0' and use pip install -c constraints.txt
   ```

## Dead Ends

- **** — Invalid syntax; pip requires comma or space between specifiers. (100% fail)
- **** — Quotes don't fix the parser error; it's about the specifier format. (90% fail)
- **** — Pip aborts the entire installation. (80% fail)