An-Introduction-to-Computer-Science/ch7.decision tree at master · CSusingPython/An-Introduction-to-Computer-Science · GitHub

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chapter 7 Decision Structures

<relop> : relational operator

1) Simple Decisions

In a program designed to be either imported (without running) or run directly,
the call to ma in at the bottom must be made conditional. A simple decision
should do the trick:

[imported]
if <condition>:
<body>

[run directly]
if <condition>:
main ( )

Whenever a module is imported, Python creates a special variable, __name__ ,
inside that module and assigns it a string representing the module's name.
>>> import math
>>> math . __name__
'math'

However, when Python code is being run directly (not imported), Python
sets the value of _..name__ to be '__main__ ' .

>>> __name__
, __ main __ ,

2) Two-Way Decisions

if <condition> :
<statements>
else :
<statements>

3) Multi-Way Decisions

if < condition1 > :
< case 1 statements>
elif < condition2> :
< case2 statements>
elif < condition3> :
< case3 statements>
...
else :
<default statements>

4. Exception Handling

try :
<body >
except <ErrorType> :
<handler>

5. Study in Design: Max of Three
Strategy 1: Compare Each to All
if x1 >= x2 and x1 >= x3 :
ma xval = x1
el if x2 >= x1 and x2 >= x3 :
ma xval - x2
el se :
ma xval - x3

Strategy 2: Decision Tree
if x1 >= x2 :
if x1 >= x3 :
maxval - x1
el se :
ma xval - x3
el se :
if x2 >= x3 :
ma xval - x2
el se :
maxval - x3

Strategy 3: Sequential Processing
ma xval = x1
if x2 > maxval:
ma xval = x2
if x3 > ma xval:
ma xval = x3

Strategy 4: Use Python
d ef ma in ( ):
x1, x2, x3 = eval ( input (" Pl ea se enter three val ues: " ) )
print (" T he la rgest val ue is", ma x (x1, x2, x3) )

* Don't be afraid to step back and think
about the overarching problem. Similarly, when designing programs, you
should always have an eye toward making your program more generally
useful.
* Don't reinvent the wheel.