Python_4_Codecademy_4_Conditiona

<a href="http://www.jianshu.com/p/54870e9541fc">总目录</a>

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课程页面：https://www.codecademy.com/
内容包含课程笔记和自己的扩展折腾

Comparators

• ==
• !=
• <
• <=
• >
• >=

Boolean operators

• and
  • true and true: true
  • true and false: false
  • false and false: false
• or
  • true or true: true
  • true or false: true
  • false or false: false
• not
  • not true: false
  • not false: true
• 如果不加括号，计算机处理就有顺序（类似orders of operations里面的pemdas），即是n->a->o.

Conditional Statement Syntax (if)

• 如果if后面的expression是True，就执行if后面的命令

if 6 + 1 != 10:
    print "abc"

• 如果if后面的fuction return的是True, 就执行if后面的命令

def addition():
    if 1 + 1 == 2:
        return True
#
def print_result():
    if addition():
        return "2"
#
print "1+1=" + print_result()

if ... else ...

• 对if进行补充。

def addition(a, b):
    if a >= b:
        print "the 1st number %s is NOT less than the 2nd number %s" % (a, b)
    else: 
        print "the 1st number %s is less than the 2nd number %s" % (a, b)
#
addition(3, 3)
addition(1, 6)
addition(6, 1)
"""
Output:
the 1st number 3 is NOT less than the 2nd number 3
the 1st number 1 is less than the 2nd number 6
the 1st number 6 is NOT less than the 2nd number 1
"""

if... elif... elif... else...

• elif满足多个if的要求。按顺序执行。

def addition(a, b):
    if a > b:
        print "the 1st number %s is greater than the 2nd number %s" % (a, b)
    elif a == b:
        print "the 1st number %s is equal to the 2nd number %s" % (a, b)
    else: 
        print "the 1st number %s is less than the 2nd number %s" % (a, b)
#
addition(3, 3)
addition(1, 6)
addition(6, 1)
"""
Output:
the 1st number 3 is equal to the 2nd number 3
the 1st number 1 is less than the 2nd number 6
the 1st number 6 is greater than the 2nd number 1
"""