【Python爬虫】-《笨办法学 Python》练习1-5

《笨办法学 Python》开启练习

1.第一个程序

print("hello world")
print("Hello Again")
print("I like typing this")
print("This is fun.")
print("Yay! Printing.")
print("I'd much rather you 'not'.")
print('I "said" do not touch this.')

此程序打印字符串，字符串单双引号的包含要错开使用，如果最外层是双引号，里层要用单引号，若外层是单引号，里层可要双引号。

2.注释和井号

代码的#中文为井号，英文为 octothorpe 或者pound character。
程序中的#号可以用于注释，也可以用注解的方式将这段代码临时禁用。

3.数字和数学运算

#打印句子 I will now count my chicken:
print(" I will now count my chicken:")
#打印Hen和25+30/6计算的值
print("Hens",25+30/6)
print("Roosters",100 - 25 * 3 % 4)
print("Now I will count the eggs:")

#打印引号中的句子
print("3 + 2 + 1 - 5 + 4 % 2 - 1 / 4 + 6")
print("Is it true that 3 + 2 < 5 - 7?")
print("3 + 2 < 5 - 7")

print("What is 3 + 2?", 3 + 2)
print("What is 5 - 7?", 5 - 7)

print("Oh, that's why it's False.")
print("How about some more.")

#打印句子：Is it greater?，并且打印5>-2判断的结果（False、True）
print("Is it greater?", 5 > -2)
print("Is it greater or equal?", 5 >= -2)
print("Is it less or equal?", 5 <= -2)

print("How about some more.")
print("Is it greater?", 5 > -2)
print("Is it greater or equal?", 5 >= -2)

在数学运算整数乘除时运算不够精确，得出结果没有小数部分，仅有整数，而浮点数能准确得出结果。

#浮点数数学运算
print("100/2.8=",100/2.8)

4.变量和命名

#定义变量名cars、pace_in_a_car 、drivers 和passengers 并分别赋值给变量名
cars = 100
space_in_a_car = 4.0
drivers = 30
passengers = 90

#变量名进行数学运算并且赋值给新的变量名
cars_not_driven = cars - drivers
cars_driven = drivers
carpool_capacity = cars_driven * space_in_a_car
average_passengers_per_car = passengers / cars_driven
#打印句子和变量名
print("There are", cars, "cars available.")
print("There are only", drivers, "drivers available.")
print("There will be", cars_not_driven, "empty cars today.")
print("We can transport", carpool_capacity, "people today.")
print("We have", passengers, "to carpool today.")
print("We need to put about", average_passengers_per_car, "in each car.")

如果在运算过程中使用未定义的变量名将出错，在使用变量名之前先定义变量名。此例子中的4.0属于浮点数，可以提高数值精度，得出准确的值。

5.更多的变量和打印

#定义特征变量名并赋值
name='Zed D.Helon'
age=30
height=70 #inches
weight=180 #lbs
eyes='blue'
teeth='White'
hair='Brown'

print("Let's talk about %s." % name)
print("He's %d inches tall." % height)
print("He's %d pounds heavy." % weight)
print("Actually that's not too heavy.")
print("He's got %s eyes and %s hair." % (eyes, hair))
print("His teeth are usually %s depending on the coffee." %
          teeth)
print("If I add %d, %d, and %d I get %d." % (age,
          height, weight, age + height +weight))

打印变量名的值，有多个值打印时要用括号（）。

print("使用变量将英寸和磅转换成厘米和千克:")
inch=180
pound=65.5
cm=inch*2.54
kg=pound*0.45392

print("If his %d inches tall,about %d cm tall."%(inch,cm))
print("If his %d pounds heavy,about %d kg heavy."%(pound,kg))

其中，1英寸=2.54厘米；1镑=0.45392千克

python字符串格式化符号:

总结

1.使用变量名前先要定义变量名，不存在的变量名、大小写字母错误和写错的变量名会报错。
2.打印字符和变量组合时候，有多个变量打印要用括号（）包含在里面。
3.字符串格式化符号要对应使用，后期在字符串方面需要多练习，尤其是字符串函数方面的。