python30题

使用python解释器(python aa.py)或在unix系统下赋值成777，执行（./aa.py）

1个byte = 8bit，在ASCII表中，一共有255个字符，一个字符占8位。

最初的计算机是由美国人发明的，制定了一张包含他们能用到的所有字符和计算机能理解的数字的对应关系。随着计算机的发展和普及，各国都制定了自己的编码，那么ASCII也容纳不了且无法形成统一标准，就推出了Unicode（万国码）。utf-8是可变长的编码，是unicode原
本占2个字节的英文被编码成1个字节，汉字是3个字节，生僻的字符占4-6个字节，节省了传输英文编写文档的空间。gbk是中国人自己的字符集，容纳了2万1千多个字符。

utf-8用6个字节表示2个汉字，gbk用4个字节

单行注释用“#”，多行注释用‘‘‘注释内容‘‘‘

（1）不能以数字开头（2）只能是字母、数字或下划线的任意组合，但不能有特殊字符（3）关键字通常不能声明为变量

id(变量名)

.pyc文件是由.py文件经过编译后生成的字节码文件，其加载速度相对于之前的.py文件有所提高，且实现了源码隐藏，以及一定程度上的反编译。一般是import其他py文件的时候会生成。

user = input("Username: ").strip()
passwd = input("Password: ").strip()
if user == "seven" and passwd == "123":
    print("Welcome to back,",user)
else:
    print("Incorrect username or password!")

for i in range(3):
    user = input("Username: ").strip()
    passwd = input("Password: ").strip()
    if user == "seven" and passwd == "123":
        print("Welcome to back,",user)
        break
    else:
        print("Incorrect username or password!")

for i in range(3):
    user = input("Username: ").strip()
    passwd = input("Password: ").strip()
    if user == "seven" or user == "alex" and passwd == "123":
        print("Welcome to back,",user)
        break
    else:
        print("Incorrect username or password!")

num = 0
for i in range(99):
    if i % 2 == 0:
        num = num - i
    else:
        num = num + i
print(num)
-49

i = 0
while i < 12:
    i +=1
    if i == 6 or i == 10:
        continue
    else:
        print(i)

i = 1
while i<=100:
    if i % 2 != 0:
        print(i)
    i +=1

i = 1
while i<=100:
    if i % 2 == 0:
        print(i)
    i +=1

101 1010 100000 111

类是抽象的概念，为所有对象定义了抽象的属性与行为，对象是类的一个具体。是一个实实在在的东西。比如人类是所有人的一个统称，具体的你、我、他是其中的对象。

n1和n2指向同一块内存地址，数值是123

开辟了2个内存地址存放数据123456，并分别起了个名称为n1和n2.

给数据123456起了另外一个别名n2，相当于n1和n2都指向该数据的内存地址

布尔值有True和False

print(a) 
alex 
print(b)
Alex

print(name.startswith("al"))
执行结果
False

print(name.endswith("X"))
执行结果
True

print(name.replace("l","p"))
执行结果
apeX

print(name.split("l"))
执行结果
[‘ a‘, ‘eX‘]

列表

print(name.upper())
执行结果
ALEX

print(name.lower())
执行结果
alex

print(name[1])
执行结果
a

print(name[:3])
执行结果
 al

print(name[-2:])
执行结果
eX

print(name.index("e"))
执行结果
3

name = " aleX"
for i in name:
    print(i)

li = ["alex","eric","rain"]
for i in li:
    print("_".join(i))

执行结果
a_l_e_x
e_r_i_c
r_a_i_n

print(len(li)) 
执行结果
3

li.append("seven")
print(li)
执行结果
[‘alex‘, ‘eric‘, ‘rain‘, ‘seven‘]

li.insert(0,"Tony")
print(li)
执行结果
[‘Tony‘, ‘alex‘, ‘eric‘, ‘rain‘]

li[1] = "Kelly"
print(li) 
执行结果
[‘alex‘, ‘Kelly‘, ‘rain‘]

li.remove("eric")
print(li)
执行结果
[‘alex‘, ‘rain‘]

>>> li.pop(1)
‘eric‘
>>> li
[‘alex‘, ‘rain‘]

>>> li = ["alex","eric","rain"]
>>> li.pop()
‘rain‘
>>> li
[‘alex‘, ‘eric‘]

>>> li = [‘alex‘, ‘eric‘, ‘rain‘, ‘seven‘]
>>> del li[1:]
>>> li
[‘alex‘]

>>> li = ["alex","eric","rain"]
>>> li.reverse()
>>> li
[‘rain‘, ‘eric‘, ‘alex‘]

li = ["alex","eric","rain"]
for index in range(len(li)):
    print(index,li[index])
执行结果
0 alex
1 eric
2 rain

li = ["alex","eric","rain"]
for index,value in enumerate(li,100):
    print(index,value)
执行结果
100 alex
101 eric
102 rain

li = ["alex","eric","rain"]
for i in li:
    for item in i:
        print(item)
执行结果
a
l
e
x
e
r
i
c
r
a
i
n

>>> li = ["hello","seven",["mon",["h","kelly"],"all"],123,446]
>>> li[2][1][1]
‘kelly‘

>>> li[2][2] = "ALL"
>>> li
[‘hello‘, ‘seven‘, [‘mon‘, [‘h‘, ‘kelly‘], ‘ALL‘], 123, 446]

>>> tu = ("alex","eric","rain")
>>> len(tu)
3

>>> tu[1]
‘eric‘

>>> tu[:2]
(‘alex‘, ‘eric‘)

tu = ("alex","eric","rain")
for i in tu:
    print(i)
执行结果
alex
eric
rain

tu = ("alex","eric","rain")
for index in range(len(tu)):
    print(index,tu[index])
执行结果
0 alex
1 eric
2 rain

tu = ("alex","eric","rain")
for index,values in enumerate(tu,10):
    print(index,values)
执行结果
10 alex
11 eric
12 rain

不可变类型,一旦一个对象被定义了,它的值就不能再被修改,如果包含可变的列表,字典等值,那这些值可以改变

不能被修改

k2对应的值是列表类型,可以被修改.
>>> tu = ("alex",[11,22,{"k1":"v1","k2":["age","name"],"k3":(11,22,33)},44])
>>> tu[1][2]["k2"].append("Seven")
>>> tu
(‘alex‘, [11, 22, {‘k1‘: ‘v1‘, ‘k2‘: [‘age‘, ‘name‘, ‘Seven‘], ‘k3‘: (11, 22, 33)}, 44])

k3对应的类型是元组,不能被修改

for keys in dic.keys():
    print(keys)
执行结果
k1
k2
k3

for values in dic.values():
   print(values)
执行结果
v1
v2
[11, 22, 33]

dic = {"k1":"v1","k2":"v2","k3":[11,22,33]}
for k,v in dic.items():
    print(k,v)
执行结果
k1 v1
k3 [11, 22, 33]
k2 v2

dic.setdefault("k4","v4")
print(dic)
执行结果
{‘k2‘: ‘v2‘, ‘k3‘: [11, 22, 33], ‘k1‘: ‘v1‘, ‘k4‘: ‘v4‘}

dic["k1"] = "alex"print(dic)执行结果{‘k3‘: [11, 22, 33], ‘k2‘: ‘v2‘, ‘k1‘: ‘alex‘}

dic["k3"].append("44")
print(dic)
执行结果
{‘k3‘: [11, 22, 33, ‘44‘], ‘k2‘: ‘v2‘, ‘k1‘: ‘v1‘}

dic["k3"][0] = "18"
print(dic)
执行结果
{‘k3‘: [‘18‘, 22, 33], ‘k2‘: ‘v2‘, ‘k1‘: ‘v1‘}

s = "alex"
print(list(s))
执行结果
[‘a‘, ‘l‘, ‘e‘, ‘x‘]

s = "alex"
print(tuple(s))
执行结果
(‘a‘, ‘l‘, ‘e‘, ‘x‘)

li = ["alex","seven"]
print(tuple(li))
执行结果
(‘alex‘, ‘seven‘)

tu = ("alex","seven")
print(list(tu))
执行结果
[‘alex‘, ‘seven‘]

li = ["alex","seven"]
dic = {}
for i,v in enumerate(li,10):
    dic.setdefault(i,v)
    print(dic)

执行结果 {‘seven‘: 11, ‘alex‘: 10}

print(n.encode(encoding="utf-8"))
执行结果
b‘\xe8\x80\x81\xe7\x94\xb7\xe5\xad\xa9‘
print("\xe8\x80\x81\xe7\x94\xb7\xe5\xad\xa9".encode(encoding="utf-8"))
执行结果
b‘\xc3\xa8\xc2\x80\xc2\x81\xc3\xa7\xc2\x94\xc2\xb7\xc3\xa5\xc2\xad\xc2\xa9‘

print(n.encode(encoding="gbk"))
执行结果
b‘\xc0\xcf\xc4\xd0\xba\xa2‘
print("\xc0\xcf\xc4\xd0\xba\xa2".encode(encoding="gbk"))
执行结果
UnicodeEncodeError: ‘gbk‘ codec can‘t encode character ‘\xc0‘ in position 0: illegal multibyte sequence

a = 0
for i in range(0,100):
    a += (i+1)
    print(a)
执行结果
5050