python入门(三)条件表达式
python入门(三)条件表达式参考书籍 python_note_pdq.pdf
4.1 布尔表达式
真值为1，假值为0
4.2 逻辑操作符
and or not
a = 1
b = 0
print(a and b) ---------- 0
print(a or b) ---------- 1
print(not a) ----------- False
if(a or b) :
print(a or b)------------1
空字符串为假，非空字符串为真，非零的数为真
and左边为真就显示右边的值
print("9" and "test") ----------test
print("test" and "haha")-----haha
or 显示真值
print("9" or "test") -----9
print("test" or "9") -----test
print(0 or "test") ------test
print("" or "9") ------9
print("===",0 or "","====")---- ============
not 相反
print(not 0) ------- True
print(not "") ------True
4.3 条件语句
Header:
First Statement
Second Statement
......
Last Statement
Other Statement
eg:
x = 16
if(x % 2 ):
print(x," is even")
else :
print(x," is odd")--------16 is even
eg:
x = 15
y = 12
if(x > y):
print("big")
elif(x == y):
print("equal")
else:
print("small") ---------big
4.4 while语句
#中文注释
x = 15
result = 0
while(x):
result = result + x
x = x - 1
print(result)
4.5 条件嵌套
eg1:
x = 12
y = 11
if(x == y):
print("equals")
else:
if(x > y):
print("large")
else:
print("small"); --------large
eg2:
x = 11
if(0<x<20):
print(x,"介于0--20之间。") ------- 11 介于0--20之间。
4.6 return语句
4.7 键盘输入
raw_input 报错如下：
NameError: name 'raw_input' is not defined
原来是python的后续版本将名字修改了为input了。
eg1:
name = input("please input something:")
print(name)
返回：
please input something:sillycat
sillycat
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