University:
Boston University
Course:
CAS CS 501 | Computer Science Practicum
Academic year:

2023
Views:

389

Pages:

17
Author:

Jaime Mckenzie

Python is a Scripting Language Flow Control 4 More control over choices 1 2 3 4 5 6 if and else: sister_age = 15 brother_age = 12 if sister_age > brother_age : print " sister is older " else : print " brother is older " block needs to be correctly indented too. else gets executed if Boolean is False. You don’t shouldn’t hit Enter twice between if code block and else statement. else Python is a Scripting Language Compound Conditionals 1 allow you to combine tests. and: True only if both are True or: True if at least one is True and and or Try these: 1 2 3 4 1 > 0 and 1 < 2 1 < 2 and " x " in " abc " " a " in " hello " or " e " in " hello " 1 <= 0 or " a " not in " abc " Python is a Scripting Language Compound Conditionals 1 - Output 1 2 3 4 5 6 7 8 >>> 1 > 0 and 1 < 2 True >>> 1 < 2 and " x " in " abc " False >>> " a " in " hello " or " e " in " hello " True >>> 1 <= 0 or " a " not in " abc " False Python is a Scripting Language Compound Conditionals 2 Try this: 1 temperature = 32 2 if temperature > 60 and temperature < 75: 3 print " It ’s nice and cozy in here ! " 4 else : 5 print " Too extreme for me . " Python is a Scripting Language Compound Conditionals 2 - Output 1 2 3 4 5 6 7 >>> >>> ... ... ... ... Too temperature = 32 if temperature > 60 and temperature < 75: print " It ’s nice and cozy in here ! " else : print " Too extreme for me . " extreme for me . Python is a Scripting Language Compound Conditions 3 And try this: 1 hour = 11 2 if hour < 7 or hour > 23: 3 print " Go away ! " 4 print " I ’m sleeping ! " 5 else : 6 print " Welcome to the cheese shop ! " 7 print " Can I interest you in some choice gouda ? " Python is a Scripting Language Compound Conditions 3 - Output 1 2 3 4 5 6 7 8 9 10 >>> hour = 11 >>> if hour < 7 or hour > 23: ... print " Go away ! " ... print " I ’m sleeping ! " ... else : ... print " Welcome to the cheese shop ! " ... print " Can I interest you in some choice gouda ? " ... Welcome to the cheese shop ! Can I interest you in some choice gouda ? Python is a Scripting Language Flow Control 5 There’s also 1 2 3 4 5 6 7 8 elif: sister_age = 15 brother_age = 12 if sister_age > brother_age : print " sister is older " elif sister_age == brother_age : print " sister and brother are the same age " else : print " brother is older " Python is a Scripting Language Flow Control 5 - Output 1 2 3 4 5 6 7 8 9 10 >>> sister_age = 15 >>> brother_age = 12 >>> if sister_age > brother_age : ... print " sister is older " ... elif sister_age == brother_age : ... print " sister and brother are the same age " ... else : ... print " brother is older " ... sister is older is not required at the end, just like in the first if example. else Python is a Scripting Language Functions Remember type()? Functions ... do some useful work, let us re-use code without having to retype it, can take some input, and optionally return a value. Python is a Scripting Language Functions Remember type()? Functions ... do some useful work, let us re-use code without having to retype it, can take some input, and optionally return a value. You call a function by using its name, followed by its arguments in parenthesis: 1 length = len ( " Mississippi " ) This assigns the number of characters in the string ”Mississippi” to the variable length. Python is a Scripting Language Functions: Step 1 Write the function signature, how it will be called: 1 def, Tells Python you’re defining a function. 2 Then a space, and the function’s name. 3 Then an open parenthesis. 4 Then a comma-separated list of parameters 5 Then a closing parenthesis. 6 And finally a colon, ’:’. 1 def myFunction (): or 1 def myFunction ( myList , myInteger ): Python is a Scripting Language Functions: Step 2 Do something (useful): Underneath the function signature you do some work. This code must be indented, just like if/else blocks. This tells python that it’s part of the function. You can use variables passed as parameters just like you used variables before 1 def add (x , y ): 2 result = x + y Python is a Scripting Language Functions: Step 3 Return something (if you want to). return tells python to return a result. 1 def add (x , y ): 2 result = x + y 3 return result or shorter.... 1 def add (x , y ): 2 return x + y In Python you can return anything: strings, booleans ... even other functions! Python is a Scripting Language Functions: Step 3 Once return is called, the work in the function ends: 1 def absoluteValue ( number ): 2 if number < 0: 3 return number * -1 4 return number Python is a Scripting Language Functions: Step 3 Once return is called, the work in the function ends: 1 def absoluteValue ( number ): 2 if number < 0: 3 return number * -1 4 return number This code have also been written like: 1 def absoluteValue ( number ): 2 if number < 0: 3 return number * -1 4 else : 5 return number Python is a Scripting Language Functions: Step 4 Use them! Again and again and again.... 1 2 3 4 5 6 7 def add (x , y ): return x + y result = add (1234 , 5678) print result result = add ( -1.5 , .5) print result

Python for Non-programmers - A Gentle Introduction 3

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