The format is as described in ICAO Doc 8126 section 5.5.2 bullet d):
In the indication of the geographical coordinates of a location: - the latitude should be given first; - symbols for degrees, minutes or seconds should be omitted; - two digits should always be used in expressing values of less than 10 degrees of latitude; and - three digits should always be used in expressing values of less than 100 degrees of longitude. For example, 050735N 0652542W means five degrees, seven minutes and thirty-five seconds North, sixty-five degrees, twenty-five minutes and forty-two seconds West.
What is typical in AIP pubblications is the additional part
of decimal seconds, like
a string representation for latitude,
a latitude in decimal degrees
This format is used in AIP pubblications, for examples for runway threshold
coordinates, stand positions, etc.
This is used also in
ALL_FT+ files from NM.
parse_lat_icao("554718N")#>  55.78833