python基础语法

1. 注释的三种形式

# print('hello world')

'''
print('hello world')
'''

"""
print('hello world')
"""

2. 基本数据类型

整形，浮点数，字符串，布尔值，空值，

print(type(20))

# 字符串
str1 = 'abc'
str2 = "abc"
str3 = '''abc'''

print(type(str1))
print(type(str2))
print(type(str3))

# 布尔值
print(type(True))

# 空值
print(type(None))

3. 变量

a = 1
print(a)

a = 'abc' # Python是弱类型语言
print(a)

4. 常量 Python 中没有真正的常量，只是按照编程习惯，把全部用大写字母表示的量作为常量，不去修改它

PI = 3.1415926

5. list

classmates = ['Michael','Bob','Tracy']

# 长度
len(classmates)

# 取值
classmates[0]
classmates[-1]

# 追加
classmates.append('adam')

# 插入元素
classmates.insert(2,'bob')

# 删除尾部元素
classmates.pop()
classmates.pop(2)

# 修改
classmates[1] = 'haha'

6. tuple 元组一旦初始化就不能修改

classmates = ('Michael','Bob','Tracy')

# 定义一个元素
t = (1,) # 不能 t = (1)

7. 条件判断

age = 3

if age >= 18:
    print('adult')
elif age >= 6:
    print('teenager')
else:
    print('kid')

8. 循环

# for
names = ['Michael','Bob','Tracy']

for name in names:
    print(name)

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

# while
n = 1
while n <= 100:
    print(n)
    n = n + 1
print('END')

# break
n = 1
while n <= 100:
    if n > 10:
        break
    print(n)
    n = n + 1
print('END')

# continue
n = 0
while n < 10:
    n += 1
    if n % n == 0:
        continue
    print(n)

9. dict

d = {'Michael':95,'Bob':97}

# 取值

d['Bob']

# 添加
d['Adam'] = 79

# 判断 key 是否在 dict 中
print('Thomas' in d)

print(d.get('Thomas'),-1) # 判断 key 是否在 d中，不在就返回 -1

10. set 里面有重复的就会自动过滤掉,是无序无重复元素的集合

s = set([1,2,3])

# 添加
s.add(4)

# 删除
s.remove(4)


# 不可变对象和可变对象
# list 是可变对象
a = ['c','b','a']
a.sort()

# 可变对象
a = 'abc'
a1 = a.replace('a','A')

print(a) # abc
print(a1) # Abc

11. 函数

# 定义函数
def my_abs(x):
    if not isinstance(x,(int,float)):
        raise  TypeError('bad operand type')
    if x >= 0:
        return x
    else:
        return -x


# 位置参数: 按照位置顺序依次给x ,n 赋值
def power(x,n):
    s = 1
    while n > 0:
        n = n - 1
        s = s * x
    return s


# 默认参数
def enroll(name,gender,age = 6,city = 'beijing'):
    print(name,gender,age,city)

'''
1.必选参数在前，默认参数在后
2.多个默认参数，不按顺序调用时，要把参数名写上 enroll('Bob','F',city='shangqiu')
3.默认参数必须指向不变对象
'''

# 可变参数 可变参数组成一个tuple
def calc(*numbers):
    sum = 0
    for n in numbers:
        sum = sum + n * n
    return sum

calc(1,2,3)
num = [1,2,3]
calc(*num)

# 关键字参数 可变参数组成一个dict
def person(name,age, **kv):
    print('name',name,'age:',age,'other:',kv)

extra = {'city':'beijing','job':'Engineer'}
person('bob',25,**extra)

# 命名关键字参数
def person(name,age,*,city,job):
    print(name,age,city,job)

12.高级特性

# 切片
L = range(100)

# 1：切片的起始位置，30切片的终止位置，4是切片的步长
for x in L[1:30:4]:
    print(x)

print('ABCDEDF'[:3])

# 列表生成式
L = [x * x for x in range(1,11)]
for x in L:
    print(x)
    
# 加入判断
[x * x for x in range(1,11) if x % 2 == 0]

# 双层循环
[m + n for m in 'ABC' for n in 'XYZ']