If the block_group is not specified it will give results for B25121_047E.

Here I did all Delaware counties and all states:

>>> import censusdata
>>> censusdata.download('acs5', 2015, censusdata.censusgeo([('state', '10'),('county', '*')]), ['B25121_047E', "B23025_005E"])
                                                    B25121_047E  B23025_005E
Kent County, Delaware: Summary level: 050, stat...         5784         6904
New Castle County, Delaware: Summary level: 050...        15081        21525
Sussex County, Delaware: Summary level: 050, st...         9040         7794
>>> censusdata.download('acs5', 2015, censusdata.censusgeo([('state', '*')]), ['B25121_047E', "B23025_005E"])
                                                    B25121_047E  B23025_005E
Alabama: Summary level: 040, state:01                    181050       207097
Alaska: Summary level: 040, state:02                      14505        31285
Arizona: Summary level: 040, state:04                    209199       275712
Arkansas: Summary level: 040, state:05                   115943       104943
California: Summary level: 040, state:06                 693825      1891081
Colorado: Summary level: 040, state:08                   148157       195578
Connecticut: Summary level: 040, state:09                 82736       172292
Delaware: Summary level: 040, state:10                    29905        36223
District of Columbia: Summary level: 040, state:11         7665        35811
Florida: Summary level: 040, state:12                    677067       915976
Georgia: Summary level: 040, state:13                    297953       468932
Hawaii: Summary level: 040, state:15                      23824        42288
Idaho: Summary level: 040, state:16                       63516        55312
Illinois: Summary level: 040, state:17                   374479       608516
Indiana: Summary level: 040, state:18                    257676       258739
Iowa: Summary level: 040, state:19                       123291        81735
Kansas: Summary level: 040, state:20                     100056        88454
Kentucky: Summary level: 040, state:21                   166805       174308
Louisiana: Summary level: 040, state:22                  147389       178150
Maine: Summary level: 040, state:23                       55229        47497
Maryland: Summary level: 040, state:24                   124810       238027
Massachusetts: Summary level: 040, state:25              138683       280164
Michigan: Summary level: 040, state:26                   390617       477746
Minnesota: Summary level: 040, state:27                  179958       167764
Mississippi: Summary level: 040, state:28                108716       138445
Missouri: Summary level: 040, state:29                   229129       226528
Montana: Summary level: 040, state:30                     39393        32361
Nebraska: Summary level: 040, state:31                    64802        47602
Nevada: Summary level: 040, state:32                      75295       148467
New Hampshire: Summary level: 040, state:33               38710        42733
New Jersey: Summary level: 040, state:34                 178992       413343
New Mexico: Summary level: 040, state:35                  70515        88924
New York: Summary level: 040, state:36                   403577       829141
North Carolina: Summary level: 040, state:37             347429       453420
North Dakota: Summary level: 040, state:38                23343        11464
Ohio: Summary level: 040, state:39                       425860       477251
Oklahoma: Summary level: 040, state:40                   138556       115978
Oregon: Summary level: 040, state:41                     122347       184016
Pennsylvania: Summary level: 040, state:42               440068       514993
Rhode Island: Summary level: 040, state:44                27377        48418
South Carolina: Summary level: 040, state:45             180518       217977
South Dakota: Summary level: 040, state:46                32399        20220
Tennessee: Summary level: 040, state:47                  244213       266297
Texas: Summary level: 040, state:48                      692935       912068
Utah: Summary level: 040, state:49                        77832        81870
Vermont: Summary level: 040, state:50                     24007        18957
Virginia: Summary level: 040, state:51                   218012       276030
Washington: Summary level: 040, state:53                 187142       277806
West Virginia: Summary level: 040, state:54               84408        63341
Wisconsin: Summary level: 040, state:55                  205733       193763
Wyoming: Summary level: 040, state:56                     18845        15002
Puerto Rico: Summary level: 040, state:72                118143       235772
>>>