utah when only passing dictthe index in the resulting series will have the dict' keys in sorted order in [ ]states ['california''ohio''oregon''texas'in [ ]obj series(sdataindex=statesin [ ]obj out[ ]california nan ohio oregon texas in this case values found in sdata were placed in the appropriate locationsbut since no value for 'californiawas foundit appears as nan (not numberwhich is considered in pandas to mark missing or na values will use the terms "missingor "nato refer to missing data the isnull and notnull functions in pandas should be used to detect missing datain [ ]pd isnull(obj out[ ]california true ohio false oregon false texas false in [ ]pd notnull(obj out[ ]california false ohio true oregon true texas true series also has these as instance methodsin [ ]obj isnull(out[ ]california true ohio false oregon false texas false discuss working with missing data in more detail later in this critical series feature for many applications is that it automatically aligns differentlyindexed data in arithmetic operationsin [ ]obj out[ ]ohio oregon texas utah in [ ]obj out[ ]california nan ohio oregon texas in [ ]obj obj out[ ]california nan ohio oregon getting started with pandas www it-ebooks info