Python WKT or Proj4 lookup package

GDAL contains the most complete open source implementation and I'm not aware of any port to Python.

Rasterio does the same kind of thing as GDAL's Python bindings and calls the same C library functions.

>>> from rasterio.crs import CRS
>>> CRS.from_epsg(4326).wkt
'GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4326"]]

Rasterio is not lightweight by any measure.

I'd use the Python bindings for GDAL and OGR. If GDAL/OGR is installed on our machine, the pcs.csv file in gdal-data directory contains an extract of the EPSG Registry about projected coordinate reference systems, so we can filter this file to obtain the result. Suppose we are interested in zone 33, here's a quick and dirty solution:

from osgeo import ogr, osr

in_ds = ogr.GetDriverByName('CSV').Open('pcs.csv')
layer = in_ds.GetLayer()
zone = '33' #'33N'
layer.SetAttributeFilter("COORD_REF_SYS_NAME LIKE '%UTM zone {0}%'".format(zone))
for feature in layer:
    code = feature.GetField("COORD_REF_SYS_CODE")
    name = feature.GetField("COORD_REF_SYS_NAME")
    srs = osr.SpatialReference()
    srs.ImportFromEPSG(int(code))
    print 'EPSG:' + code + ' - ' + name
    print 'Proj4: ', srs.ExportToProj4()
    print 'WKT: ', srs.ExportToWkt()
    print

Note: we can refine the search choosing also the hemisphere (e.g. 33N) changing the value of the zone variable in the code.

This is an extract of the result:

EPSG:2078 - ELD79 / UTM zone 33N
Proj4:  +proj=utm +zone=33 +ellps=intl +towgs84=-115.8543,-99.0583,-152.4616,0,0,0,0 +units=m +no_defs 
WKT:  PROJCS["ELD79 / UTM zone 33N",GEOGCS["ELD79",DATUM["European_Libyan_Datum_1979",SPHEROID["International 1924",6378388,297,AUTHORITY["EPSG","7022"]],TOWGS84[-115.8543,-99.0583,-152.4616,0,0,0,0],AUTHORITY["EPSG","6159"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4159"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",15],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Easting",EAST],AXIS["Northing",NORTH],AUTHORITY["EPSG","2078"]]

EPSG:2312 - Garoua / UTM zone 33N
Proj4:  +proj=utm +zone=33 +ellps=clrk80 +units=m +no_defs 
WKT:  PROJCS["Garoua / UTM zone 33N",GEOGCS["Garoua",DATUM["Garoua",SPHEROID["Clarke 1880 (RGS)",6378249.145,293.465,AUTHORITY["EPSG","7012"]],AUTHORITY["EPSG","6197"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4197"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",15],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Easting",EAST],AXIS["Northing",NORTH],AUTHORITY["EPSG","2312"]]

EPSG:2313 - Kousseri / UTM zone 33N
Proj4:  +proj=utm +zone=33 +ellps=clrk80 +units=m +no_defs 
WKT:  PROJCS["Kousseri / UTM zone 33N",GEOGCS["Kousseri",DATUM["Kousseri",SPHEROID["Clarke 1880 (RGS)",6378249.145,293.465,AUTHORITY["EPSG","7012"]],AUTHORITY["EPSG","6198"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4198"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",15],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Easting",EAST],AXIS["Northing",NORTH],AUTHORITY["EPSG","2313"]]