arduino/Arduino · error · TypeError

sep must be None or a string

Error message

sep must be None or a string

What it means

six.print_ is the Python 2 emulation of the print() function. Its sep keyword must be None, a str, or a unicode string; passing any other type (int, list, bytes-like object in a Py2 context, etc.) raises this TypeError before any output is produced.

Source

Thrown at arduino-core/src/processing/app/i18n/python/requests/packages/urllib3/packages/six.py:350

""")


    def print_(*args, **kwargs):
        """The new-style print function."""
        fp = kwargs.pop("file", sys.stdout)
        if fp is None:
            return
        def write(data):
            if not isinstance(data, basestring):
                data = str(data)
            fp.write(data)
        want_unicode = False
        sep = kwargs.pop("sep", None)
        if sep is not None:
            if isinstance(sep, unicode):
                want_unicode = True
            elif not isinstance(sep, str):
                raise TypeError("sep must be None or a string")
        end = kwargs.pop("end", None)
        if end is not None:
            if isinstance(end, unicode):
                want_unicode = True
            elif not isinstance(end, str):
                raise TypeError("end must be None or a string")
        if kwargs:
            raise TypeError("invalid keyword arguments to print()")
        if not want_unicode:
            for arg in args:
                if isinstance(arg, unicode):
                    want_unicode = True
                    break
        if want_unicode:
            newline = unicode("\n")
            space = unicode(" ")
        else:
            newline = "\n"

View on GitHub (pinned to a0df6e0e83)

Solutions

1. Pass a string separator: sep=', ' or sep=None.
2. Coerce non-string separators before the call: sep=str(value) or sep=', '.join(parts).
3. Drop the sep argument entirely and rely on the default single space.

Example fix

// before
six.print_('a', 'b', sep=['-'])
// after
six.print_('a', 'b', sep='-')

if sep is not None and not isinstance(sep, (str, unicode)):
    sep = str(sep)

def is_valid_sep(sep):
    return sep is None or isinstance(sep, (str, unicode))

try:
    six.print_(*args, sep=sep)
except TypeError as e:
    if 'sep must be None or a string' in str(e):
        six.print_(*args, sep=str(sep))
    else:
        raise

When it happens

Trigger: six.print_('a', 'b', sep=1); passing a list/tuple as sep; passing sep=None-like sentinel objects that are not str/unicode.

Common situations: Programmatically building separator values from config; translating Python 3 code where sep accepts anything str()-able; mixing bytes and text on Python 2.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• end must be None or a string
• invalid keyword arguments to print()
• expected at most 1 arguments, got %d
• update() takes at most 2 positional arguments (%d given)
• update() takes at least 1 argument (0 given)

AI-assisted analysis of arduino/Arduino@a0df6e0e83 (2026-09-06). Data as JSON: /api/errors/27d2b4f3b2e4ef8c. Report an issue: GitHub.