I mean that the language doesn't prefer a single way, as opposed to programmers' conventions.
Fredrik> it's more than just a convention -- built-in functions and Fredrik> operators always return 0 for false and 1 for true whenever Fredrik> they need to invent a boolean value. this is documented in Fredrik> the language reference.
On the other hand, the library isn't nearly so consistent. Just for fun, I started browsing the library documentation at random.
The very first page I visited was the description of gc, the garbage collector interface. The first function that returns a truth value there is described as
isenabled() Returns true if automatic collection is enabled.
Some more examples:
184.108.40.206 String Methods
endswith(suffix[,start[,end]]) Return true if the string ends with the specified suffix, otherwise return false.
Similarly for isalnum, isalpha, isdigit, islower, isspace.
2.2.8 File Objects:
isatty() Return true if the file is connected to a tty(-like) device, else false.
6.2 os.path -- Common pathname manipulations
exists(path) Return true if path refers to an existing path.
I'm sure there are others.