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== Conditional statements with if ==
If statements are used to implement decisions and branching in the program. They must contain an 'if' block, and optionally one or many 'elif' and an 'else' block:

<source lang="python">
if fruit == 'apple':
price = 0.55
elif fruit == 'banana':
price = 0.75
elif fruit == 'orange':
price = 0.80
else:
print 'we dont have %s'%(fruit)
</source>

== Boolean value of variables ==
Each variable can be interpreted as boolean logic. All values are treated as True, except for:

<source lang="python">
False
0
[]
''
{}
None
</source>

== Code blocks ==
* After an if statement, all indented commands are treated as a code block, and are executed if the condition applies.
* The next unindented command Is executed in any case.

== Comparison operators ==
An expression may contain any combination of:

* a == b, a != b (equality)
* a < b, a > b, a <= b, a >= b (relations)
* a or b, a and b, not a (boolean logic)
* (a or b) and (c or d) (priority)
* a in b (inclusion, when b is a list)