Python Syntax Soup: x in y
Python has these operators to check if a key exist in hash table or element exist in list:
x in list
x not in list
There are several issues:
x not in list is not necessary. It can be done with
not (x in list)
not is part of
not in operator. This means, the word
not has context dependent semantics.
not in is a operator. Using English words as operator is not so good. but now that operator is 2 words, separated by space! So, syntactically, it becomes not distinguishable from statements.
x in y is subform the loop form
for x in y
, and also the
[… for x in y]
. This is a example of context dependent semantics.
k in d is itself is not necessary. Python has a
has_key() method for dictionary, which is in sync with the 20 other dictionary methods.
Method syntax is systematic and also informative of its meaning because of the name.
Though, strangely, python decided to deprecate it, and in python 3, it's gone.
This is the state of the affair of syntax soup. When you learn a language, there's little governing principle of what symbol can go where (as in formal language), instead, you learn by rote of what symbols or words can go where in what context means what.
Here is another example.
the python import statement syntax, is a prime example of context dependent semantics. witness:
from aa import bb
in the above, the two
import name have different meaning.
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