自学python笔记_简书 python?

除法与整除区别

a = 3 / 2
print(a) # 1.5
a = 3 // 2
print(a) # 1

变量赋值

a = 'ABC'
b = a
a = 'XYZ'
print(b) #ABC

格式化输出

print('%2d-%02d' % (3, 1))
print('%.2f' % 3.1415926)

list

classmates = ['Michael', 'Bob', 'Tracy']
print(classmates[0])
print(classmates)
print(classmates[3])

classmates = ['Michael', 'Bob', 'Tracy']
print(classmates[0])
print(classmates)
print(classmates[-1])
print(classmates[-2])
a = len(classmates)
print(a)
classmates.append('Adam') #尾部插入
print(classmates)
classmates.pop() #删减
print(classmates)
classmates.insert(1, "Jack") #中间插入
print(classmates)
classmates.pop(1)
print(classmates)

怎么通过命令行执行python文件：

if 判断

age = 20
if age > 18:
    print("age is %d" % age)
    print("age is %d", age) #错误
else:
    print("age is too small")

birth = input("birth is : ")
s = int(birth)
if s > 2000:
    print("00 after")
else:
    print("00 ahead")

注意input返回的是字符串
for 循环语句

sum = 0
count = [1, 2, 3, 4, 5, 6, 7, 8]
for x in count:
    sum = sum + x
print(sum)

range函数的使用

sum = 0
for x in range(101):
    sum = sum + x
print(sum)

while 循环用法：

count = 99
sum = 0
while count > 0:
    sum = sum + count
    count = count - 2
print(sum)

加上break后的用法：

count = 99
sum = 0
while count > 0:
    sum = sum + count
    count = count - 2
    print(count)
    if sum > 500:
        break
print(sum)

continue 的用法：跳过当前循环，即continue以后的语句

count = 11
while count > 0:
    count = count - 1
    if count % 3 == 0:
       continue
    print(count)
print("END")

字典的用法：dict

d = {'jack': 10, 'tom': 20, 'ver': 30}
print(d['jack'])
d['jack'] = 100
print(d['jack'])
d.pop('jack')
if d.get('jack', -1) == -1:
    print('jack is delete')

set的用法：一个无序和无重复元素的集合，添加重复元素将不起作用。

a = [1, 2, 4, 5, 6, 6]
s = set(a)
print(s)
s.add(4)
print(s)
s.add(8)
print(s)

s2 = set([2, 4])
print(s & s2)

def my_test(x):
    if x > 20:
        print('x is small')
    elif x < 10:
        print('x is so small')
    else:
        print('x is between 10 with 20')
my_test(30)