ERROR: Invalid requirement: ... (requirement spec parse error)

What This Error Means

pip could not parse a requirement specifier (malformed version constraint, quotes/smart-quotes, comments, or an invalid line in a requirements file).

How to Fix It

1. Fix invalid specifiers: use name==1.2.3 (pin) or name>=1.2,<2 (range).
2. If you need extras, quote the whole argument: python -m pip install "transformers[sentencepiece,torch]".
3. Remove or properly comment out lines in requirements files (comments must start with # at the beginning of the line or after whitespace).
4. If you're unsure what versions exist, search the package index or consult the package's release history, then pin a real version instead of words like latest.

Why It Happens

• A requirement contains invalid version syntax (for example pip== with no version).
• A requirement line contains smart quotes (“ / ”) or mismatched quotes (common on Windows shells).
• A comment or placeholder like #todo is not formatted as a comment in the current context.
• Version constraints are malformed (for example mixing < and >= without a comma separator).

How to Verify

1. Re-run python -m pip install ... and confirm the Invalid requirement error is gone.
2. If using a requirements file, run python -m pip install -r requirements.txt and confirm it parses past the previously failing line.

Manual requirements parsing checks

1. If installing from a file, open it and find the exact line pip reports (run with -v to see more context).
2. Remove smart quotes and retype quotes using plain ASCII " or '.
3. If you copied a multiline command, ensure line continuations match your shell.

Common CLI Output

ERROR: Invalid requirement: 'pip==': Expected end or semicolon (after name and no valid version specifier)

ERROR: Invalid requirement: 'transformers[sentencepiece,torch]<4.26>=4.23.0': Expected end or semicolon (after version specifier)

ERROR: Invalid requirement: '#'

ERROR: Invalid requirement: "'transformers[torch]'": Expected package name at the start of dependency specifier

ERROR: Invalid requirement: "“isaacsim[all,extscache]==4.5.0”": Expected package name at the start of dependency specifier

How pip parses requirement specifiers

1. pip expects requirements in a specific format, such as name, name==version, name>=1.2,<2, or name[extra]==version.
2. If a requirement contains invalid syntax (like a trailing ==), smart quotes from copy/paste, or a malformed constraint line, pip fails fast with an Invalid requirement error.

Prevention Tips

• Keep requirements files machine-generated when possible (constraints/lock tooling) and avoid manual editing mistakes.
• Avoid smart quotes by copying commands from plain text sources.
• Prefer one requirement per line with simple specifiers and commas between constraints (e.g. >= and <).

Where This Can Be Triggered

def install_req_from_req_string(
    req_string: str,
    comes_from: InstallRequirement | None = None,
    isolated: bool = False,
    user_supplied: bool = False,
) -> InstallRequirement:
    try:
        req = get_requirement(req_string)
    except InvalidRequirement as exc:
        raise InstallationError(f"Invalid requirement: {req_string!r}: {exc}")