Would it not be better to describe the differences between C and Python
variables directly rather than using an analogy?
In C, a variable is the address of a storage location that contains its
value. If that value is itself an address then the variable is described
as a pointer.
In Python, a variable is a reference to an object that has a type as
well as a value.
The statement:
a= b = c;
results in three separate values in C but only one in Python. The
effect is the same in both languages provided that c refers to a
constant. However, if c is a mutable object, such as a list, then
changing the value of one variable changes them all. Anyone coming to
Python from C may be confused by this as it is not clearly described in
any of the books on Python that I have read.
When passing an argument to a function, C uses pass-by-value whereas
Python uses what is in effect pass-by-reference. In order to obtain
pass-by-reference in C the value must be a pointer. Inside the function
the pointer must be dereferenced by prefixing it with an asterisk to
obtain the value.
Eur Ing Christopher Thoday
Software Engineer
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