The locale module uses locale alias table derived from X11 locale.alias file for mapping bare locale names without encodings to locale names with encodings. However sometimes glibc default encoding for a locale differs from that used in X11 locale.alias.

Here is full differences table:

                 GLibc                 X11 locale.alias

az_az            az_AZ.UTF-8           az_AZ.ISO8859-9E
ca_ad            ca_AD.ISO8859-15      ca_AD.ISO8859-1
ca_fr            ca_FR.ISO8859-15      ca_FR.ISO8859-1
ca_it            ca_IT.ISO8859-15      ca_IT.ISO8859-1
cy_gb            cy_GB.ISO8859-14      cy_GB.ISO8859-1
en_in            en_IN.UTF-8           en_IN.ISO8859-1
et_ee            et_EE.ISO8859-1       et_EE.ISO8859-15
fi_fi            fi_FI.ISO8859-1       fi_FI.ISO8859-15
gd_gb            gd_GB.ISO8859-15      gd_GB.ISO8859-1
hi_in            hi_IN.UTF-8           hi_IN.ISCII-DEV
iu_ca            iu_CA.UTF-8           iu_CA.NUNACOM-8
iw_il            iw_IL.ISO8859-8       he_IL.ISO8859-8
ka_ge            ka_GE.GEORGIAN_PS     ka_GE.GEORGIAN-ACADEMY
lo_la            lo_LA.UTF-8           lo_LA.MULELAO-1
mi_nz            mi_NZ.ISO8859-13      mi_NZ.ISO8859-1
nr_za            nr_ZA.UTF-8           nr_ZA.ISO8859-1
nso_za           nso_ZA.UTF-8          nso_ZA.ISO8859-15
ru_ru            ru_RU.ISO8859-5       ru_RU.UTF-8
rw_rw            rw_RW.UTF-8           rw_RW.ISO8859-1
sq_al            sq_AL.ISO8859-1       sq_AL.ISO8859-2
ss_za            ss_ZA.UTF-8           ss_ZA.ISO8859-1
ta_in            ta_IN.UTF-8           ta_IN.TSCII-0
tg_tj            tg_TJ.KOI8_T          tg_TJ.KOI8-C
th_th            th_TH.TIS_620         th_TH.ISO8859-11
tn_za            tn_ZA.UTF-8           tn_ZA.ISO8859-15
ts_za            ts_ZA.UTF-8           ts_ZA.ISO8859-1
tt_ru            tt_RU.UTF-8           tt_RU.TATAR-CYR
ur_pk            ur_PK.UTF-8           ur_PK.CP1256
uz_uz            uz_UZ.ISO8859-1       uz_UZ.UTF-8
uz_uz@cyrillic   uz_UZ.UTF-8@cyrillic  uz_UZ.UTF-8
vi_vn            vi_VN.UTF-8           vi_VN.TCVN
zh_cn            zh_CN.GB2312          zh_CN.gb2312
zh_tw            zh_TW.BIG5            zh_TW.big5
zh_tw.euctw      zh_TW.EUC_TW          zh_TW.eucTW

For example with the en_IN encoding:

>>> import locale, _locale
>>> _locale.setlocale(locale.LC_CTYPE)
'en_IN'
>>> locale.getlocale()
('en_IN', 'ISO8859-1')
>>> locale.nl_langinfo(locale.CODESET)
'UTF-8'
>>> locale.setlocale(locale.LC_CTYPE, locale.getlocale())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/serhiy/py/cpython/Lib/locale.py", line 592, in setlocale
    return _setlocale(category, locale)
locale.Error: unsupported locale setting