Python_day4

• python3的字符串:

　　1.文本字符串(str)---->unicode

''
""
''' '''
str()

　　2.二进制字符串(bytes)

b''
b""
b''' '''
bytes()

　　3.编码:

str--->bytes
string.encode(encoding = 'utf-8')

　　4.解码:

bytes--->str
bytestring.decode(encodeing = 'utf-8')

　　5.练习

s = 'python是最好的语言'
bs = s.encode()
print(type(bs))
print(bs)

bs2 = bytes(s, encoding='utf-8')
print(type(bs2))
print(bs2)

s1 = bs2.decode()
print(type(s1))
print(s1)

s2 = str(bs2, encoding='utf-8')
print(type(s2))
print(s2)

• 字符串方法补充

# 居中填充
s = 'python'
s = s.center(20, '-')
print(s)
# 统计出现个数
print(s.count('th', 0, 3))
# 找到子串 '-------python-------'
ind = s.find('th')
print(ind)
# 按进制输出
s = '{:b}'.format(10)
print(s)

s = '{:o}'.format(10)
print(s)

s = '{:x}'.format(10)
print(s)

import random
# 字符串拼接 
s = 'beautiful'
l = list(s)
random.shuffle(l)
s = ''.join(l)
print(s)

s = ''.join(('haha', 'hehe', 'hihi'))
print(s)

s = ','.join('hello')
print(s)
# 替换
s = s.replace(',', '.')
print(s)
# 切割
res = s.split('.')
print(res)

• 深复制和浅复制

　　import copy　

# 对于非复合类型 深复制和浅复制无差别
a = 10
b = copy.copy(a)
print(id(a))
print(id(b))
a = 20
print(a, b)

# 对于可变复合类型 浅复制不会复制子对象,而深复制会
a = [1,2,[100, 200]]
b = copy.copy(a)
print(id(a))
print(id(b))
a[0] = 110
print(a)
print(b)
a[2][1] = 222
print(a)
print(b)

b = copy.deepcopy(a)
print(id(a))
print(id(b))
a[0] = 1
print(b)
a[2][1] = 333
print(a)
print(b)

print(id(a[2]))
print(id(b[2]))

• 列表生成式

l = []

for i in range(100):
	if i % 2 == 0:
		l.append(i)
print(l)

l = [i*i for i in range(100) if i % 2 == 0]
print(l)

'''
练习1:有字符串s1 = 'ABC' s2 = 'xyz' 生成一个列表，列表中的元素是['Ax', 'By', 'Cz']
'''
l = [x+y for x in 'ABC' for y in 'xyz']
print(l)

s1 = 'ABC'
s2 = 'xyz'
l = [s1[i]+s2[i] for i in range(len(s1))]
print(l)

'''
练习2:有列表l = ['Hello', 'EVERYone', 'goOd', 'AFTErNooN']
	使用一条语句将列表中变成由所有小写字母组成
'''
l = ['Hello', 'EVERYone', 'goOd', 'AFTErNooN']
l = [x.lower() for x in l]
print(l)

• 生成器

l = [i for i in range(100)]
print(l)　

# 生成器：节省空间
g = (i for i in range(100))
print(g)

print(next(g))
print(next(g))

for x in g:
	print(x, end=' ')
print()

• 字典(dict):

# 定义
d1 = {'name':'python', 'age':20}
print(type(d1))
print(d1)

d2 = dict(name='python', age=20)
print(type(d2))
print(d2)

d3 = dict([('name', 'python'), ('age', 20)])
print(type(d3))
print(d3)

d4 = dict(zip(['name', 'age'], ['python', 20]))
print(type(d4))
print(d4)

# 通过key得到成员: key唯一的,不可变的
print(d4['name'])

d4['name'] = 'guido'
print(d4)

# 获得所有的key, values, item
print(d4.keys())

print(d4.values())

print(d4.items())

# 遍历
for k in d4.keys():
	print(d4[k])

for k, v in d4.items():
	print(k, v)

for k in d4: # key
	print(k)

# 增加
d4['height'] = 180
print(d4)

d4.update(id=5, score=100)
print(d4)

# 删除
d4.pop('id')
print(d4)

• 集合(set):无序的不重叠的可变的

　　去除重复

# 定义
st = {1,2,3,4}
print(type(st))
print(st)

# 去重
l = [1,2,3,3,2,34,1,23]
l = list(set(l))
print(l)

for i in st:
	print(i)

st.add(100)
print(st)

st.pop()
print(st)

st.remove(100)
print(st)

st2 = {2,1,8,9,4}
print(st & st2) # 交集
print(st | st2) # 并集
print(st - st2) # 差集
print(st ^ st2) # 交叉差集