Issue 1:
Code Sample, a copy-pastable example if possible

In [2]: mi = pd.MultiIndex.from_product([[0, 1]]*2, names=[('first', 'level'), ('second', 'level')])

In [3]: mi.droplevel(('first', 'level'))
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
~/nobackup/repo/pandas/pandas/core/indexes/multi.py in _get_level_number(self, level)
775 'level number' % level)
--> 776 level = self.names.index(level)
777 except ValueError:

ValueError: 'first' is not in list

During handling of the above exception, another exception occurred:

KeyError Traceback (most recent call last)
<ipython-input-3-1952401ac0fc> in <module>()
----> 1 mi.droplevel(('first', 'level'))

~/nobackup/repo/pandas/pandas/core/indexes/base.py in droplevel(self, level)
3177 level = [level]
3178
-> 3179 levnums = sorted(self._get_level_number(lev) for lev in level)[::-1]
3180
3181 if len(level) == 0:

~/nobackup/repo/pandas/pandas/core/indexes/base.py in <genexpr>(.0)
3177 level = [level]
3178
-> 3179 levnums = sorted(self._get_level_number(lev) for lev in level)[::-1]
3180
3181 if len(level) == 0:

~/nobackup/repo/pandas/pandas/core/indexes/multi.py in _get_level_number(self, level)
777 except ValueError:
778 if not isinstance(level, int):
--> 779 raise KeyError('Level %s not found' % str(level))
780 elif level < 0:
781 level += self.nlevels

KeyError: 'Level first not found'

In [4]: mi.droplevel([('first', 'level')])
Out[4]: Int64Index([0, 1, 0, 1], dtype='int64', name=('second', 'level'))

Problem description

Always the same story: if we allow users to pass tuples of stuff interchangeably with lists of stuff, then tuples as values (or names, as in this case) will cause problems.

Expected Output

Out[4]

... as long as we all agree that the level argument can accept lists of names but not tuples of names. The only other option I see is to document that droplevel does not support tuple names (except as items of a list).

Output of pd.show_versions()

INSTALLED VERSIONS

commit: None

python: 3.5.3.final.0

python-bits: 64

OS: Linux

OS-release: 4.9.0-6-amd64

machine: x86_64

processor:

byteorder: little

LC_ALL: None

LANG: it_IT.UTF-8

LOCALE: it_IT.UTF-8

pandas: 0.24.0.dev0+14.g489cc24c8.dirty

pytest: 3.5.0

pip: 9.0.1

setuptools: 39.0.1

Cython: 0.25.2

numpy: 1.14.1

scipy: 0.19.0

pyarrow: None

xarray: None

IPython: 6.2.1

sphinx: 1.5.6

patsy: 0.5.0

dateutil: 2.7.0

pytz: 2017.2

blosc: None

bottleneck: 1.2.0dev

tables: 3.3.0

numexpr: 2.6.1

feather: 0.3.1

matplotlib: 2.0.0

openpyxl: 2.3.0

xlrd: 1.0.0

xlwt: 1.3.0

xlsxwriter: 0.9.6

lxml: 4.1.1

bs4: 4.5.3

html5lib: 0.999999999

sqlalchemy: 1.0.15

pymysql: None

psycopg2: None

jinja2: 2.10

s3fs: None

fastparquet: None

pandas_gbq: None

pandas_datareader: 0.2.1

Issue 2:
Code Sample, a copy-pastable example if possible

In [2]: mi = pd.MultiIndex.from_product([[0, 1]]*2, names=[('first', 'level'), ('second', 'level')])

In [3]: mi.droplevel(('first', 'level'))
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
~/nobackup/repo/pandas/pandas/core/indexes/multi.py in _get_level_number(self, level)
775 'level number' % level)
--> 776 level = self.names.index(level)
777 except ValueError:

ValueError: 'first' is not in list

During handling of the above exception, another exception occurred:

KeyError Traceback (most recent call last)
<ipython-input-3-1952401ac0fc> in <module>()
----> 1 mi.droplevel(('first', 'level'))

~/nobackup/repo/pandas/pandas/core/indexes/base.py in droplevel(self, level)
3177 level = [level]
3178
-> 3179 levnums = sorted(self._get_level_number(lev) for lev in level)[::-1]
3180
3181 if len(level) == 0:

~/nobackup/repo/pandas/pandas/core/indexes/base.py in <genexpr>(.0)
3177 level = [level]
3178
-> 3179 levnums = sorted(self._get_level_number(lev) for lev in level)[::-1]
3180
3181 if len(level) == 0:

~/nobackup/repo/pandas/pandas/core/indexes/multi.py in _get_level_number(self, level)
777 except ValueError:
778 if not isinstance(level, int):
--> 779 raise KeyError('Level %s not found' % str(level))
780 elif level < 0:
781 level += self.nlevels

KeyError: 'Level first not found'

In [4]: mi.droplevel([('first', 'level')])
Out[4]: Int64Index([0, 1, 0, 1], dtype='int64', name=('second', 'level'))

Problem description

Always the same story: if we allow users to pass tuples of stuff interchangeably with lists of stuff, then tuples as values (or names, as in this case) will cause problems.

Expected Output

Out[4]

... as long as we all agree that the level argument can accept lists of names but not tuples of names. The only other option I see is to document that droplevel does not support tuple names (except as items of a list).

Output of pd.show_versions()

INSTALLED VERSIONS

commit: None

python: 3.5.3.final.0

python-bits: 64

OS: Linux

OS-release: 4.9.0-6-amd64

machine: x86_64

processor:

byteorder: little

LC_ALL: None

LANG: it_IT.UTF-8

LOCALE: it_IT.UTF-8

pandas: 0.24.0.dev0+14.g489cc24c8.dirty

pytest: 3.5.0

pip: 9.0.1

setuptools: 39.0.1

Cython: 0.25.2

numpy: 1.14.1

scipy: 0.19.0

pyarrow: None

xarray: None

IPython: 6.2.1

sphinx: 1.5.6

patsy: 0.5.0

dateutil: 2.7.0

pytz: 2017.2

blosc: None

bottleneck: 1.2.0dev

tables: 3.3.0

numexpr: 2.6.1

feather: 0.3.1

matplotlib: 2.0.0

openpyxl: 2.3.0

xlrd: 1.0.0

xlwt: 1.3.0

xlsxwriter: 0.9.6

lxml: 4.1.1

bs4: 4.5.3

html5lib: 0.999999999

sqlalchemy: 1.0.15

pymysql: None

psycopg2: None

jinja2: 2.10

s3fs: None

fastparquet: None

pandas_gbq: None

pandas_datareader: 0.2.1