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BUG: Unclear error message assign a column with an empty DataFrame #55956
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Why are you expecting the provided lambda to get called? E.g.
does not raise an error. In your case, there are now rows to iterate over, so you get an empty DataFrame.
|
I understand that the right side produces an empty DataFrame and it is the assignment that fails. |
Assigning an empty data frame is fine, as long as it only has one column: df1 = pd.DataFrame()
df1["test1"] = pd.DataFrame() # the same ValueError as in the issue
df2 = pd.DataFrame()
df2["test1"] = pd.DataFrame(columns=["column"]) # successfully creates an empty "test1" column
df3 = pd.DataFrame()
df3["test1"] = pd.DataFrame(columns=["column1", "column2]) # fails with the same Value Error The "multiple columns" error message is written for the third case, but is raised in your zero-column case as well. Would you find the error clearer if it said something like "Cannot set a DataFrame without any columns to the single column test1"? |
Thanks @rob-sil - agreed the error message can be approved. |
Has this issue been fixed? I still encountered this issue in the latest version |
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Edit: This turned out to be an issue with the error message when setting a single column using a DataFrame with no columns; see #55956 (comment) - rhshadach
Pandas version checks
I have checked that this issue has not already been reported.
I have confirmed this bug exists on the latest version of pandas.
I have confirmed this bug exists on the main branch of pandas.
Reproducible Example
Issue Description
I was expecting to see
KeyError 'test'
as an error, but I get an error as follows:Expected Behavior
I was expecting to see
KeyError 'test'
in the error tracebackInstalled Versions
Python 3.10.9, pandas 2.1.3, numpy 1.24.3 - Windows 10
ImportError Traceback (most recent call last)
Cell In[6], line 1
----> 1 pd.show_versions()
File ~\AppData\Local\anaconda3\lib\site-packages\pandas\util_print_versions.py:141, in show_versions(as_json)
104 """
105 Provide useful information, important for bug reports.
106
(...)
138 ...
139 """
140 sys_info = _get_sys_info()
--> 141 deps = _get_dependency_info()
143 if as_json:
144 j = {"system": sys_info, "dependencies": deps}
File ~\AppData\Local\anaconda3\lib\site-packages\pandas\util_print_versions.py:98, in _get_dependency_info()
96 result: dict[str, JSONSerializable] = {}
97 for modname in deps:
---> 98 mod = import_optional_dependency(modname, errors="ignore")
99 result[modname] = get_version(mod) if mod else None
100 return result
File ~\AppData\Local\anaconda3\lib\site-packages\pandas\compat_optional.py:147, in import_optional_dependency(name, extra, errors, min_version)
145 minimum_version = min_version if min_version is not None else VERSIONS.get(parent)
146 if minimum_version:
--> 147 version = get_version(module_to_get)
148 if version and Version(version) < Version(minimum_version):
149 msg = (
150 f"Pandas requires version '{minimum_version}' or newer of '{parent}' "
151 f"(version '{version}' currently installed)."
152 )
File ~\AppData\Local\anaconda3\lib\site-packages\pandas\compat_optional.py:74, in get_version(module)
71 version = getattr(module, "version", None)
73 if version is None:
---> 74 raise ImportError(f"Can't determine version for {module.name}")
75 if module.name == "psycopg2":
76 # psycopg2 appends " (dt dec pq3 ext lo64)" to it's version
77 version = version.split()[0]
ImportError: Can't determine version for xlrd
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