{"record":{"id":"37a7ba8fb84c0742","repo":"pandas-dev/pandas","slug":"invalid-value-for-dtype-str-value-should-be-a-s","errorCode":null,"errorMessage":"Invalid value for dtype 'str'. Value should be a string or missing value (or array of those).","messagePattern":"Invalid value for dtype 'str'\\. Value should be a string or missing value \\(or array of those\\)\\.","errorType":"exception","errorClass":"TypeError","httpStatus":null,"severity":"error","filePath":"pandas/core/arrays/string_.py","lineNumber":863,"sourceCode":"                value = self.dtype.na_value\n            elif not isinstance(value, str):\n                raise TypeError(\n                    f\"Invalid value '{value}' for dtype '{self.dtype}'. Value should \"\n                    f\"be a string or missing value, got '{type(value).__name__}' \"\n                    \"instead.\"\n                )\n        else:\n            value = extract_array(value, extract_numpy=True)\n            if not is_array_like_deprecate_non_pandas(value):\n                value = np.asarray(value, dtype=object)\n            elif isinstance(value.dtype, type(self.dtype)):\n                return value\n            else:\n                # cast categories and friends to arrays to see if values are\n                # compatible, compatibility with arrow backed strings\n                value = np.asarray(value)\n            if len(value) and not lib.is_string_array(value, skipna=True):\n                raise TypeError(\n                    \"Invalid value for dtype 'str'. Value should be a \"\n                    \"string or missing value (or array of those).\"\n                )\n        return value\n\n    def __setitem__(self, key, value) -> None:\n        if self._readonly:\n            raise ValueError(\"Cannot modify read-only array\")\n\n        value = self._validate_setitem_value(value)\n\n        key = check_array_indexer(self, key)\n        scalar_key = lib.is_scalar(key)\n        scalar_value = lib.is_scalar(value)\n        if scalar_key and not scalar_value:\n            raise ValueError(\"setting an array element with a sequence.\")\n\n        if not scalar_value:","sourceCodeStart":845,"sourceCodeEnd":881,"githubUrl":"https://github.com/pandas-dev/pandas/blob/71959b8cb9b2459c16e14b34f28b178ccfe14735/pandas/core/arrays/string_.py#L845-L881","documentation":"When _validate_setitem_value receives a non-scalar (array-like) value, it checks every element with lib.is_string_array(value, skipna=True). If any element is neither a str nor NA-like, it raises TypeError with the generic 'dtype str' message. This guards bulk assignment like arr[mask] = [...].","triggerScenarios":"Calling string_array[[0,1]] = [1, 2], string_array[:] = ['a', 3], or assigning a list/array containing non-string, non-NA elements to multiple positions.","commonSituations":"Bulk-updating a string column from a numeric intermediate; assigning the output of a mapping that returned mixed types.","solutions":["Convert every element to str before bulk assignment: [str(v) for v in values].","Replace missing entries with pd.NA or np.nan rather than non-string sentinels.","Use pd.array(values, dtype='string') to build a coerced array, then assign it."],"exampleFix":"// before\nstring_array[[0, 1]] = [1, 2]\n\n// after\nstring_array[[0, 1]] = [str(1), str(2)]","handlingStrategy":"validation","validationCode":"clean = [str(v) if not (pd.isna(v) or isinstance(v, str)) else v for v in values]\nstring_array[key] = clean","typeGuard":"import pandas as pd\n\ndef all_strings_or_na_array(values) -> bool:\n    return all(isinstance(v, str) or pd.isna(v) for v in values)","tryCatchPattern":null,"preventionTips":["Coerce every element to str before bulk assignment.","Build a coerced pd.array(values, dtype='string') and assign that.","Replace missing entries with pd.NA rather than non-string sentinels."],"tags":["string-array","setitem","type-error","bulk-assign"],"analyzedSha":"71959b8cb9b2459c16e14b34f28b178ccfe14735","analyzedAt":"2026-08-07T01:30:20.476Z","schemaVersion":2},"datasetVersion":"2026-08-07T03:17:09.362Z"}