《Python for Beginners》学习笔记（3）
《Python for Beginners》为LearnStreet上的Python入门课程。本节主要学习内容为条件语句。
Lesson 4 Control Flow and Conditionals
1. 第一个Python函数
1 def check_wounds(): 2 #your code here 3 arms = 0 4 if arms == 1: 5 return "tis but a scratch" 6 elif arms == 0: 7 return "flesh wound" 8 else: 9 return "cross bridge" 10 11 #This is just for you to see what happens when the function is called 12 print check_wounds()
输出结果：
flesh wound
2. if语句
1 def always_true(): 2 if 1 == 1: 3 #insert your code here 4 return "complete" 5 6 #This is just for you to see what happens when the function is called 7 print always_true()
输出结果：
complete
3. 再来一个if语句
1 flag = "unchanged" 2 def always_false(): 3 global flag 4 if 1==2: 5 flag = "changed" 6 7 #This is just for you to see what happens when the function is called 8 always_false() 9 print flag
输出结果：
unchanged
4. else语句
1 def check_condition(): 2 #return this if the condition is True 3 ifRun = "if code block run" 4 5 #return this is if the condition is False 6 elseRun = "else code block run" 7 8 condition = 0 9 10 if condition == True: 11 #your code here 12 return ifRun 13 else: 14 #your code here 15 return elseRun 16 17 #This is just for you to see what happens when the function is called 18 print check_condition()
输出结果：
else code block run
5. elif语句
1 def colorful_conditions(): 2 3 color = "blue" 4 5 if color == "red": 6 return "first block" 7 elif color == "white": 8 return "second block" 9 elif color == "blue": 10 return "third block" 11 else: 12 return "fourth block" 13 14 #This is just for you to see what happens when the function is called 15 print colorful_conditions()
输出结果：
third block
6. if语句练习
问题：
When the string phrase is fewer than 30 characters long, return 1. When it is exactly 30 return 2, and when it is greater than 30 return 3.
代码：
1 def check_length(phrase): 2 # your if condition here 3 if len(phrase) < 30: 4 return 1 5 # your elif condition here 6 elif len(phrase) == 30: 7 return 2 8 # your else condition here 9 else: 10 return 3 11 12 #This is just for you to see what happens when the function is called 13 print check_length("hi, i am a phrase")
输出结果：
1
7. if语句练习2
1 """ 2 This function should check the value of the num variable and 3 return the string representation of the interval it is in Use if, elif, 4 and else statements to check if num falls in the range 1-5, 6-10, 5 11-15, or 16-20. Then return the correct interval as a string, like 6 "1-5", "6-10", "11-15", or "16-20". 7 """ 8 def check_interval(): 9 #Your code here 10 num = 5 11 if num < 6: 12 return "1-5" 13 elif num < 11: 14 return "6-10" 15 elif num < 16: 16 return "11-15" 17 else: 18 return "16-20" 19 20 #This is just for you to see what happens when the function is called 21 print check_interval()
输出结果：
1-5
8. and操作符
1 def should_eat(hungry, awake): 2 #your if statement here 3 if hungry and awake: 4 return "eat" 5 else: 6 return "don't eat" 7 8 #This is just for you to see what happens when the function is called 9 print should_eat(True, True)
输出结果：
eat
9. or操作符
1 def kitchen_or_bed(hungry, thirsty): 2 # your if statement here 3 if hungry or thirsty: 4 return "go to kitchen" 5 else: 6 return "go to bed" 7 8 #This is just for you to see what happens when the function is called 9 print kitchen_or_bed(True, True)
输出结果：
go to kitchen
10. 复习
1 def who_are_you(green, large): 2 # Write if-elif-else statements below 3 if green and large: 4 return "hulk" 5 elif green: 6 return "alien" 7 elif large: 8 return "elephant" 9 else: 10 return "Bruce Banner" 11 12 #This is just for you to see what happens when the function is called 13 print who_are_you(True, True)
输出结果：
hulk
总结：
1）注意缩进的格式
2）#开头为注释一行代码
3）注意函数定义以及条件语句后面的冒号
4）字符串可以直接作为函数的实参
（本文完）
