pandas-dev/pandas · error · TypeError

Cannot construct a ' ' from

Error message

Cannot construct a '{cls.__name__}' from '{string}'

What it means

Thrown by StringDtype.construct_from_string in pandas/core/arrays/string_.py:309 when the input string does not match any of the recognized spellings ('string', 'str' under future infer_string, 'string[python]', 'string[pyarrow]'). The fall-through else branch raises TypeError listing the offending string so the dtype registry can treat it as 'not a StringDtype name'.

Solutions

  1. Use a supported spelling: 'string', 'string[python]', or 'string[pyarrow]'.
  2. If you meant plain Python strings, use dtype='object' or enable pd.options.future.infer_string = True then use 'str'.
  3. Double-check the spelling against the docstring table in StringDtype.construct_from_string.

Example fix

// before
pd.StringDtype.construct_from_string('string[arrow]')  # typo, raises

// after
pd.StringDtype.construct_from_string('string[pyarrow]')
Defensive patterns

Strategy: validation

Validate before calling

VALID = {'string', 'string[python]', 'string[pyarrow]'}
def safe_construct(name):
    if name not in VALID:
        raise ValueError(f'{name!r} not in {VALID}')
    return pd.StringDtype.construct_from_string(name)

Type guard

null

Try / catch

try:
    return pd.StringDtype.construct_from_string(name)
except TypeError:
    return None  # fall back to object dtype

Prevention

When it happens

Trigger: Passing 'string[numpy]', 'object', 'category', 'str' (when infer_string is not enabled), 'string[arrow]' (typo), or any unrecognized dtype name to construct_from_string. Indirectly triggered by pd.api.types.pandas_dtype('string[foo]').

Common situations: Typo in a dtype string in a config file or constructor call. Using 'str' as a dtype name without enabling the future infer_string behavior. Third-party code passing a stale spelling removed in a pandas upgrade.

Related errors

AI-assisted analysis of pandas-dev/pandas@3b7651241d (2026-08-11). Data as JSON: /api/errors/f38fa69fe2a80240. Report an issue: GitHub.

Appendix: source

Thrown at pandas/core/arrays/string_.py:309

        Raise
        -----
        TypeError
            If the string is not a valid option.
        """
        if not isinstance(string, str):
            raise TypeError(
                f"'construct_from_string' expects a string, got {type(string)}"
            )
        if string == "string":
            return cls()
        elif string == "str" and using_string_dtype():
            return cls(na_value=np.nan)
        elif string == "string[python]":
            return cls(storage="python")
        elif string == "string[pyarrow]":
            return cls(storage="pyarrow")
        else:
            raise TypeError(f"Cannot construct a '{cls.__name__}' from '{string}'")

    def construct_array_type(self) -> type_t[BaseStringArray]:
        """
        Return the array type associated with this dtype.

        Returns
        -------
        type
        """
        from pandas.core.arrays.string_arrow import (
            ArrowStringArray,
        )

        if self.storage == "python" and self._na_value is libmissing.NA:
            return StringArray
        elif self.storage == "pyarrow" and self._na_value is libmissing.NA:
            return ArrowStringArray
        elif self.storage == "python":

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