Python基础

目录

　　声明变量

　　类型转换

　　四则运算

　　列表List

　　循环

　　判断

　　字典

　　文件IO

　　函数

---

 

声明变量

　　

# -*- coding: utf-8 -*-
#整数
a = 10
print(a)
#浮点数
b = 10.1
print(b)
#字符串
c = "aaa10"
print(c)

print(type(a))
print(type(b))
print(type(c))
'''
10
10.1
aaa10
<class 'int'>
<class 'float'>
<class 'str'>
'''

 

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类型转换 

 

# -*- coding: utf-8 -*-
a = "10"
b = int(a)
c = float(a)
print(b)
print(c)
print(type(b))
print(type(c))

'''
10
10.0
<class 'int'>
<class 'float'>
'''

 

 

 

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四则运算 

 

# -*- coding: utf-8 -*-
a = 2
b = 3
print(a + b)
print(a - b)
print(a * b)
print(a / b)
print(a ** b) #a的b次方

'''
5
-1
6
0.6666666666666666
8
'''

 

 

 

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列表List 

  

# -*- coding: utf-8 -*-
print("---------------声明与添加元素：-----------------")
a = []
print(a)
print(type(a))
a.append("你好")
a.append(3)
print(a)
'''
[]
<class 'list'>
['你好', 3]
'''

print("---------------list索引与长度：-----------------")
a = [2,4,6,8]
print("list的长度是：" + str(len(a)))
print(a[0])
print(a[1])
print(a[2])
print(a[3])
print(a[-1]) #打印最后一个元素
'''
list的长度是：4
2
4
6
8
8
'''

print("---------------list切片：-----------------")
a = [2,4,6,8,10]
print(a[1:3]) 
print(a[1:-1]) 
print(a[:3])
print(a[1:])
'''
[4, 6]
[4, 6, 8]
[2, 4, 6]
[4, 6, 8, 10]
'''

print("---------------遍历list：-----------------")
a = [1,3,5,7]
print("迭代器方式：")
for i in a:
    print(i)

print("遍历下标方式：")
for i in range(len(a)):
    print(a[i])
'''
迭代器方式：
1
3
5
7
遍历下标方式：
1
3
5
7
'''


print("---------------判断元素是否在list：-----------------")
a = [1,3,5,7]
print(1 in a)
#True

 

 

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循环 

 

 

# -*- coding: utf-8 -*-
a = [2,4,6,8]

for i in a:
    print(i)
'''
2
4
6
8
'''
    
for i in range(5):
    print(i)
'''
0
1
2
3
4
'''
    
k = 1
while k<=3:
    print(k)
    k += 1
'''
1
2
3
'''

 

 

 

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判断 

 

 

# -*- coding: utf-8 -*-
a = True
b = False
print(type(a))
#<class 'bool'>

a = 1
b = 2
print(a!=b)
#True

if a > b:
    print("a大于b")
elif a < b:
    print("a小于b")
else:
    print("a等于b")
#a小于b

 

 

 

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字典 

 

 

# -*- coding: utf-8 -*-
print("---------------声明与添加元素：-----------------")
a = {}
print(a)
print(type(a))
a["Java"] = 1
a["Python"] = 2
a["Python"] = 3
print(a)
'''
{}
<class 'dict'>
{'Java': 1, 'Python': 3}
'''

print("---------------dict索引与长度：-----------------")
a = {'Java': 1, 'Python': 2}
print("dict的长度是：" + str(len(a)))
print(a['Java'])
print(a['Python'])
'''
dict的长度是：2
1
2
'''

print("---------------遍历dict：-----------------")
a = {'Java': 1, 'Python': 2, 'Scala': 3}

for i in a.items():
    print(i)
'''
('Java', 1)
('Python', 2)
('Scala', 3)
'''

print("---------------返回dict的keys和values：-----------------")
a = {'Java': 1, 'Python': 2, 'Scala': 3}

print(a.keys())
print(a.values())
# dict_keys(['Java', 'Python', 'Scala'])
# dict_values([1, 2, 3])

print("---------------应用：统计出现次数：-----------------")
X = ['Java','Java','Python','Python','Python','Scala','Scala']
a = {}
for x in X:
    res = a.get(x)
    if res == None:
        a[x] = 1
    else:
        a[x] += 1
print(a)
# {'Java': 2, 'Python': 3, 'Scala': 2}
# 注意: 这样的实现方式效率最高，因为dict的查询复杂度是O(1); List查询复杂度是O(n)

 

 

 

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文件IO 

 

 

# -*- coding: utf-8 -*-
a = open("a.txt", encoding='UTF-8')
for i in a:
    print(i)
a.close()

b = open("b.txt", "w", encoding='UTF-8')
b.write("aa\n")
b.write("bb\n")
b.write("cc\n")
b.close()

 

      

 

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函数 

 

 

# -*- coding: utf-8 -*-
def m1(name, age=5):
    h = 6
    if age > h:
        print(name + "已经" + str(age) + "岁了，到了上小学的年龄")
    else:
        print(name + "只有" + str(age) + "岁，还不能上小学")

m1("tom", 2)
m1("peter")
m1("tom", 10)
'''
tom只有2岁，还不能上小学
peter只有5岁，还不能上小学
tom已经10岁了，到了上小学的年龄
'''

 

 

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