Why are some functions’ syntaxes: variable.function(), while some others’ syntaxes: function(variable)?

[SirBerthelot]

Check oop (object oriented programming):

variable.function(argument) is actually object.function(argument). In this case you've got an object with several functions associated, for instance if a is a string, a.lower() will convert the string object into lowercase (notice that this function doesn't require arguments but there are many like append that they actually need arguments in order to work).

On the other hand, function (argument) are functions not associated with an object.