there are about names in the listso we have omitted most of them those that begin with capital letter are the names of python' built-in exceptionsthe rest are function and data type names the second convention concerns the use of underscores (_names that begin and end with two underscores (such as __lt__should not be used python defines various special methods and variables that use such names (and in the case of special methodswe can reimplement themthat ismake our own versions of them)but we should not introduce new names of this kind ourselves we will cover such names in names that begin with one or two leading underscores (and that don' end with two underscoresare treated specially in some contexts we will show when to use names with single leading underscore in and when to use those with two leading underscores in single underscore on its own can be used as an identifierand inside an interactive interpreter or python shell_ holds the result of the last expression that was evaluated in normal running program no existsunless we use it explicitly in our code some programmers like to use in for in loops when they don' care about the items being looped over for examplefor in ( )print("hello"import be awarehoweverthat those who write programs that are internationalized often use as the name of their translation function they do this so that instead of writing gettext gettext("translate me")they can write ("translate me"(for this code to work we must have first imported the gettext module so that we can access the module' gettext(function let' look at some valid identifiers in snippet of code written by spanishspeaking programmer the code assumes we have done import math and that the variables radio and vieja_area have been created earlier in the programp math pi nueva_area radio radio if abs(nueva_area vieja_areaeprint("las areas han convergido"we've used the math moduleset epsilon (eto be very small floating-point numberand used the abs(function to get the absolute value of the difference between the areas--we cover all of these later in this what we are concerned with here is that we are free to use accented characters and greek letters for identifiers we could just as easily create identifiers using arabicchinesehebrewjapaneseand russian charactersor indeed characters from any other language supported by the unicode character set import