Python Variables and Assignments
Quiz yourself by thinking what should be in
each of the black spaces below before clicking
on it to display the answer.
Help!
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| variable assignment | <variable> = <expression>
<expression> right of the = assignment operator is evaluated
resulting value is stored in an object of the appropriate type
object is assigned to <variable>
variable refers to object or is bound to the object
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| reassignment of variable | Subsequent assignments to a, such as
>>> a = 6
will reuse the existing name a. The result of this assignment is that variable 'a' will refer to another object, integer object 6.
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| immutable | a = 6 does not change integer object 3.
New integer object 6 is created, and variable 'a' now refers to it.
Cannot change value of 3.
All Python number types (bool, int, float, and complex) and strings cannot be changed
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| mutable | list object can change. For example:
>>> d = [2, 3, 5, 8, 11]
>>> d[3] = 7
>>> d
[2, 3, 5, 7, 11]
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| swapping | >>> a = 6
>>> b = 3
>>> a, b = b, a
>>> a
3
>>> b
6
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| passing reference to immutable object in parameter call | a = 3
def g(x):
x=5
g(a)
a=5
a = 3
in the context of g(a), a = 5
in the larger program interactive shell a=3
function cannot reassign a to int object 5
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| passing reference to mutable object in parameter call | Functions can modify mutable arguments.
like lists
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