pypa/pip · error · SyntaxError

invalid constraint: %s

Error message

invalid constraint: %s

What it means

Raised by get_versions() inside parse_requirement() after a comma separating multiple version constraints. Once a comma is consumed, the next token must begin with a comparison operator (matched by COMPARE_OP); if it does not, the constraint list is considered invalid and a SyntaxError is raised. It guards the 'op ver, op ver' chaining syntax of PEP 508 version specifiers.

Source

Thrown at src/pip/_vendor/distlib/util.py:223

                    while True:
                        op = m.groups()[0]
                        ver_remaining = ver_remaining[m.end():]
                        m = VERSION_IDENTIFIER.match(ver_remaining)
                        if not m:
                            raise SyntaxError('invalid version: %s' % ver_remaining)
                        v = m.groups()[0]
                        versions.append((op, v))
                        ver_remaining = ver_remaining[m.end():]
                        if not ver_remaining or ver_remaining[0] != ',':
                            break
                        ver_remaining = ver_remaining[1:].lstrip()
                        # Some packages have a trailing comma which would break things
                        # See issue #148
                        if not ver_remaining:
                            break
                        m = COMPARE_OP.match(ver_remaining)
                        if not m:
                            raise SyntaxError('invalid constraint: %s' % ver_remaining)
                    if not versions:
                        versions = None
                return versions, ver_remaining

            if remaining[0] != '(':
                versions, remaining = get_versions(remaining)
            else:
                i = remaining.find(')', 1)
                if i < 0:
                    raise SyntaxError('unterminated parenthesis: %s' % remaining)
                s = remaining[1:i]
                remaining = remaining[i + 1:].lstrip()
                # As a special diversion from PEP 508, allow a version number
                # a.b.c in parentheses as a synonym for ~= a.b.c (because this
                # is allowed in earlier PEPs)
                if COMPARE_OP.match(s):
                    versions, _ = get_versions(s)
                else:

View on GitHub (pinned to d7d0d0a394)

Solutions

1. Repeat the operator before each comma-separated version: 'pkg >= 1.0, < 2.0'.
2. Check the substring after 'invalid constraint:' to find the offending token and fix or remove it.
3. When constructing compound constraints programmatically, always emit '<op> <ver>' pairs joined by ', '.

Example fix

// before
parse_requirement('django >= 4.0, 5.0')
// after
parse_requirement('django >= 4.0, < 5.0')

import re
def validate_compound_constraint(spec):
    # ensure each comma-separated piece starts with a compare operator
    body = spec.split(';', 1)[0]
    m = re.search(r'\((.*)\)', body)
    if not m:
        return True
    for piece in m.group(1).split(','):
        if not re.match(r'\s*(==|!=|<=|>=|~=|<|>)\s*\S', piece):
            return False
    return True

from distlib.util import parse_requirement
try:
    parse_requirement(line)
except SyntaxError as e:
    if 'invalid constraint' in str(e):
        reject_line(line, e)
    else:
        raise

When it happens

Trigger: parse_requirement('pkg >= 1.0 2.0'), parse_requirement('pkg >= 1.0, 2.0'), or any specifier list where a comma-separated element omits the leading operator or contains junk between constraints.

Common situations: Authors writing 'pkg >= 1.0, 2.0' (forgetting the second operator), or automated tools that join version filters with commas without re-emitting operators.

Related errors

• invalid version: %s
• invalid requirement: %s
• unexpected trailing data: %s
• Invalid requirement: {req_as_string!r}: {exc}
• Invalid requirement: {req_string!r}: {exc}

AI-assisted analysis of pypa/pip@d7d0d0a394 (2026-08-04). Data as JSON: /data/errors/8a6fa6e008db6744.json. Report an issue: GitHub.