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if the judge
- 1
if 判断条件1:
执行语句1......
else:
执行语句2……
- Also it can be rewritten as a row
执行语句1...... if 判断语句1 else 执行语句2......
- 2
if 判断条件1:
执行语句1……
elif 判断条件2: #判断条件多，用多个elif
执行语句2……
elif 判断条件3:
执行语句3……
else:
执行语句4……
- 3
a = 10
if a % 2 == 0:
print('a是偶数')
else:
print('a是奇数')
print('a = %d' % a) #不论a对2取余等于什么，都执行
#a是偶数
a = 10
and（&） or（|）
- Judgment result is true, can be converted to 1, is false, 0 can be converted to
- And is connected with, can be used multiplication operator, and that is really true = 1 (true), true and false = 0 (false), and false false = 0 (false), it can be seen there is a false end result is false, The first is a fake behind do not read, it must be false
- Or connected with, the addition can be considered, i.e., true or real = 2> 0 (true), true or false = 1 (true), false or false = 0 (false), there can be seen the final result is a true true The first one is really behind do not read, it must be true
Example 1
a = 10
print(a)
if a > 0 and a % 2 == 0: #1 * 1 = 1真
print('a是大于0的偶数')
if a > 10 and a % 2 == 0: #0 * 1 = 0假 #第一个为假，一定是假
print('a是大于10的偶数')
else: #if为假，执行else，即下行代码
print('a不是大于10的偶数')
a = 9
print(a)
if a % 2 == 1 or a < 10: #1 + 1 = 2>0真 #第一个为真，一定是真
print('a小于10或者a是奇数')
if a % 2 == 0 or a < 10: #0 + 1 = 1真 #有一个为真，一定是真
print('a小于10或者a是偶数')
if a % 2 == 0 or a > 10: #0 + 0 = 0假 #两个都假最终结果才为假
print('a是偶数或者a大于10')
else:
print('a既不是偶数又小于10')
#10
a是大于0的偶数
a不是大于10的偶数
9
a小于10或者a是奇数
a小于10或者a是偶数
a既不是偶数又小于10
Example 2
# 在不加括号时候, and优先级大于or
a = True | True & False
print(a)
# and中含0，返回0； 均为非0时，返回后一个值，
a = 5 and 7 and 6
"""
a = 5
a = 7
a = 6
"""
print(a)
# or中， 至少有一个非0时，返回第一个非0
a = 5 and 4 or 6 and 7
"""
a = (5 and 4) or (6 and 7)
a = 4 or 7
"""
print(a)
a = 4 or 7
print(a)
if not
- if not a:
- If the assignment is not a return value or None, following statement is executed
- With a previously assigned, or can be used to determine whether the return value is null
a = ''
if not a:
print('a不能为空或None')
else:
print(a)
#a不能为空或None
cycle
- Recycling ideas
- The number of cycles (while the number of cycles determined by the conditions), where the design may not know how many times
- What do recycle
- How changes in variables
while
- grammar
while 条件:
条件满足时，做的事情1
条件满足时，做的事情2
......
- From 1 to 100
i = 1
sum = 0
while i <= 100:
sum += i
i += 1
print(sum)
- * Draw a rectangle with
y = 1
while y <= 10: #为了输出十行
x = 1
while x <= 10: #为了在一行输出十个星号
print('*',end = '')
x += 1
print('')
y += 1
print('矩形完成')
#**********
**********
**********
**********
**********
**********
**********
**********
**********
**********
矩形完成
for
- grammar
for 临时变量 in 列表或字符串/元组/字典/set（集合）等:
循环满足条件时执行的代码
else:
循环不满足条件时执行的代码
- Case
for i in 'xiaoge':
print(i)
else:
print('没有内容了')
- Case
for i in range(9): #range(9)表示range(0,9)，左闭右开，从[0,9)中依次取值
print(i)
Multiplication table
while
i = 1
while i < 10:
j = 1
while j <= i:
print('%d x %d = %d\t' % (j,i,i*j),end='')
j += 1
print('')
i += 1
for
for i in range(9):
i += 1
for j in range(1,i+1):
print('%d x %d = %d\t' % (j,i,i * j),end = '') #end = ''用于不换行
print('\n')
while True break continue
- In the cycle, you may be forced to exit the loop early
age = int(input('请输入年龄：'))
i = 1
while True:
if i == age:
print('年龄为：%d' % age)
break
else:
print('猜错了，继续猜')
i += 1
- With this statement is the core idea is that if something goes wrong, you can continue to cycle
- while True loop statement must have a break, otherwise it is infinite loop has been executed
- continue to terminate the present cycle is, for the next cycle
i = 0
while i < 10:
i += 1
if i % 2 == 0:
print('%d是偶数' % i)
continue
print('当前的i是:%d' % i)
else: #i=10时，不满足while，执行else
print('else表示不满足条件时调用的代码，这时i为%d'%i)
while and else may be used, similar effects and if else
* Printing with inverted triangle
- The first line, before the leftmost asterisk with no spaces, there is a second line, the third line has two ...
while True:
i = int(input('请输入三角形行数(不超过5)：'))
if i > 5:
print('输入的数不能大于5！请重新输入！')
continue
j = 1
while i > 0:
print(' ' * (j-1) + '* ' * i )
j += 1
i -= 1
break
