python-练习

hexo -

• 优化+花俏： https://www.liaofuzhan.com/posts/1599400735.html

41-字符串格式化
“%s is %s years old” % (‘bob’, 23) # 常用
“%s is %d years old” % (‘bob’, 23) # 常用
“%s is %d years old” % (‘bob’, 23.5) # %d是整数 常用
“%s is %f years old” % (‘bob’, 23.5)
“%s is %5.2f years old” % (‘bob’, 23.5) # %5.2f是宽度为5，2位小数
“97 is %c” % 97
“11 is %#o” % 11 # %#o表示有前缀的8进制
“11 is %#x” % 11
“%10s%5s” % (‘name’, ‘age’) # %10s表示总宽度为10，右对齐, 常用
“%10s%5s” % (‘bob’, 25)
“%10s%5s” % (‘alice’, 23)
“%-10s%-5s” % (‘name’, ‘age’) # %-10s表示左对齐, 常用
“%-10s%-5s” % (‘bob’, 25)
“%10d” % 123
“%010d” % 123

"{} is {} years old".format('bob', 25)
"{1} is {0} years old".format(25, 'bob')
"{:<10}{:<8}".format('name', 'age')

42-shutil模块常用方法
import shutil

with open('/etc/passwd', 'rb') as sfobj:
    with open('/tmp/mima.txt', 'wb') as dfobj:
        shutil.copyfileobj(sfobj, dfobj) # 拷贝文件对象

shutil.copyfile('/etc/passwd', '/tmp/mima2.txt')
shutil.copy('/etc/shadow', '/tmp/')  # cp /etc/shadow /tmp/
shutil.copy2('/etc/shadow', '/tmp/')  # cp -p /etc/shadow /tmp/
shutil.move('/tmp/mima.txt', '/var/tmp/')  # mv /tmp/mima.txt /var/tmp/
shutil.copytree('/etc/security', '/tmp/anquan') # cp -r /etc/security /tmp/anquan
shutil.rmtree('/tmp/anquan')  # rm -rf /tmp/anquan
# 将mima2.txt的权限设置成与/etc/shadow一样
shutil.copymode('/etc/shadow', '/tmp/mima2.txt')
# 将mima2.txt的元数据设置成与/etc/shadow一样
# 元数据使用stat /etc/shadow查看
shutil.copystat('/etc/shadow', '/tmp/mima2.txt')
shutil.chown('/tmp/mima2.txt', user='zhangsan', group='zhangsan')

43-练习：生成文本文件
import os

def get_fname():
    while True:
        fname = input('filename: ')
        if not os.path.exists(fname):
            break
        print('%s already exists. Try again' % fname)

    return fname

def get_content():
    content = []
    print('输入数据，输入end结束')
    while True:
        line = input('> ')
        if line == 'end':
            break
        content.append(line)

    return content

def wfile(fname, content):
    with open(fname, 'w') as fobj:
        fobj.writelines(content)

if __name__ == '__main__':
    fname = get_fname()
    content = get_content()
    content = ['%s\n' % line for line in content]
    wfile(fname, content)

44-列表方法
alist = [1, 2, 3, ‘bob’, ‘alice’]
alist[0] = 10
alist[1:3] = [20, 30]
alist[2:2] = [22, 24, 26, 28]
alist.append(100)
alist.remove(24) # 删除第一个24
alist.index(‘bob’) # 返回下标
blist = alist.copy() # 相当于blist = alist[:]
alist.insert(1, 15) # 向下标为1的位置插入数字15
alist.pop() # 默认弹出最后一项
alist.pop(2) # 弹出下标为2的项目
alist.pop(alist.index(‘bob’))
alist.sort()
alist.reverse()
alist.count(20) # 统计20在列表中出现的次数
alist.clear() # 清空
alist.append(‘new’)
alist.extend(‘new’)
alist.extend([‘hello’, ‘world’, ‘hehe’])

45-检查合法标识符
import sys
import keyword
import string

first_chs = string.ascii_letters + '_'
all_chs = first_chs + string.digits

def check_id(idt):
    if keyword.iskeyword(idt):
        return "%s is keyword" % idt

    if idt[0] not in first_chs:
        return "1st invalid"

    for ind, ch in enumerate(idt[1:]):
        if ch not in all_chs:
            return "char in postion #%s invalid" % (ind + 2)

    return "%s is valid" % idt


if __name__ == '__main__':
    print(check_id(sys.argv[1]))  # python3 checkid.py abc@123

46-创建用户，设置随机密码
randpass模块参见《37-生成密码/验证码》

import subprocess
import sys
from randpass import gen_pass

def adduser(username, password, fname):
    data = """user information:
%s: %s
"""
    subprocess.call('useradd %s' % username, shell=True)
    subprocess.call(
        'echo %s | passwd --stdin %s' % (password, username),
        shell=True
    )
    with open(fname, 'a') as fobj:
        fobj.write(data % (username, password))

if __name__ == '__main__':
    username = sys.argv[1]
    password = gen_pass()
    adduser(username, password, '/tmp/user.txt')
# python3 adduser.py john

47-列表练习：模拟栈操作
stack = []

def push_it():
    item = input('item to push: ')
    stack.append(item)

def pop_it():
    if stack:
        print("from stack popped %s" % stack.pop())

def view_it():
    print(stack)

def show_menu():
    cmds = {'0': push_it, '1': pop_it, '2': view_it}  # 将函数存入字典
    prompt = """(0) push it
(1) pop it
(2) view it
(3) exit
Please input your choice(0/1/2/3): """

    while True:
        # input()得到字符串，用strip()去除两端空白，再取下标为0的字符
        choice = input(prompt).strip()[0]
        if choice not in '0123':
            print('Invalid input. Try again.')
            continue

        if choice == '3':
            break

        cmds[choice]()


if __name__ == '__main__':
    show_menu()

48-实现Linux系统中unix2dos功能
import sys

def unix2dos(fname):
    dst_fname = fname + '.txt'

    with open(fname) as src_fobj:
        with open(dst_fname, 'w') as dst_fobj:
            for line in src_fobj:
                line = line.rstrip() + '\r\n'
                dst_fobj.write(line)


if __name__ == '__main__':
    unix2dos(sys.argv[1])

49-动画程序：@从一行#中穿过
\r是回车不换行
import time

length = 19
count = 0

while True:
    print('\r%s@%s' % ('#' * count, '#' * (length - count)), end='')
    try:
        time.sleep(0.3)
    except KeyboardInterrupt:
        print('\nBye-bye')
        break
    if count == length:
        count = 0
    count += 1

50-字典基础用法
adict = dict() # {}
dict([‘ab’, ‘cd’])
bdict = dict([(‘name’, ‘bob’),(‘age’, 25)])
{}.fromkeys([‘zhangsan’, ‘lisi’, ‘wangwu’], 11)

for key in bdict:
    print('%s: %s' % (key, bdict[key]))

print("%(name)s: %(age)s" % bdict)

bdict['name'] = 'tom'
bdict['email'] = 'tom@tedu.cn'

del bdict['email']
bdict.pop('age')
bdict.clear()

51-字典常用方法
adict = dict([(‘name’, ‘bob’),(‘age’, 25)])
len(adict)
hash(10) # 判断给定的数据是不是不可变的，不可变数据才能作为key
adict.keys()
adict.values()
adict.items()
# get方法常用，重要
adict.get(‘name’) # 取出字典中name对应的value，如果没有返回None
print(adict.get(‘qq’)) # None
print(adict.get(‘qq’, ‘not found’)) # 没有qq，返回指定内容
print(adict.get(‘age’, ‘not found’))
adict.update({‘phone’: ‘13455667788’})

52-集合常用方法

集合相当于是无值的字典，所以也用{}表示

myset = set('hello')
len(myset)
for ch in myset:
    print(ch)

aset = set('abc')
bset = set('cde')
aset & bset  # 交集
aset.intersection(bset)  # 交集
aset | bset  # 并集
aset.union(bset)  # 并集
aset - bset  # 差补
aset.difference(bset)  # 差补
aset.add('new')
aset.update(['aaa', 'bbb'])
aset.remove('bbb')
cset = set('abcde')
dset = set('bcd')
cset.issuperset(dset)  # cset是dset的超集么？
cset.issubset(dset)  # cset是dset的子集么？

53-集合实例：取出第二个文件有，第一个文件没有的行
# cp /etc/passwd .
# cp /etc/passwd mima
# vim mima -> 修改，与passwd有些区别

with open('passwd') as fobj:
    aset = set(fobj)

with open('mima') as fobj:
    bset = set(fobj)

with open('diff.txt', 'w') as fobj:
    fobj.writelines(bset - aset)

54-字典练习：模拟注册/登陆
import getpass

userdb = {}

def register():
    username = input('username: ')
    if username in userdb:
        print('%s already exists.' % username)
    else:
        password = input('password: ')
        userdb[username] = password

def login():
    username = input('username: ')
    password = getpass.getpass("password: ")
    if userdb.get(username) != password:
        print('login failed')
    else:
        print('login successful')


def show_menu():
    cmds = {'0': register, '1': login}
    prompt = """(0) register
(1) login
(2) exit
Please input your choice(0/1/2): """

    while True:
        choice = input(prompt).strip()[0]
        if choice not in '012':
            print('Invalid inupt. Try again.')
            continue
        if choice == '2':
            break

        cmds[choice]()

if __name__ == '__main__':
    show_menu()

55-计算千万次加法运算时间
import time

result = 0
start = time.time()  # 返回运算前时间戳
for i in range(10000000):
    result += i
end = time.time()   # 返回运算后时间戳
print(result)
print(end - start)

56-时间相关模块常用方法
import time

t = time.localtime()  # 返回当前时间的九元组
time.gmtime()  # 返回格林威治0时区当前时间的九元组
time.time()  # 常用，与1970-1-1 8:00之间的秒数，时间戳
time.mktime(t)  # 把九元组时间转成时间戳
time.sleep(1)
time.asctime()  # 如果有参数，是九元组形式
time.ctime()  # 返回当前时间，参数是时间戳，常用
time.strftime("%Y-%m-%d") # 常用
time.strptime('2018-07-20', "%Y-%m-%d")  # 返回九元组时间格式
time.strftime('%H:%M:%S')

###########################################
from datetime import datetime
from datetime import timedelta
datetime.today()  # 返回当前时间的datetime对象
datetime.now()  # 同上，可以用时区作参数
datetime.strptime('2018/06/30', '%Y/%m/%d')  # 返回datetime对象
dt = datetime.today()
datetime.ctime(dt)
datetime.strftime(dt, "%Y%m%d")

days = timedelta(days=90, hours=3)  # 常用
dt2 = dt + days
dt2.year
dt2.month
dt2.day
dt2.hour

57-os模块常用方法
import os

os.getcwd()  # 显示当前路径
os.listdir()  # ls -a
os.listdir('/tmp')  # ls -a /tmp
os.mkdir('/tmp/mydemo')  # mkdir /tmp/mydemo
os.chdir('/tmp/mydemo')  # cd /tmp/mydemo
os.listdir()
os.mknod('test.txt')  # touch test.txt
os.symlink('/etc/hosts', 'zhuji')  # ln -s /etc/hosts zhuji
os.path.isfile('test.txt')  # 判断test.txt是不是文件
os.path.islink('zhuji')  # 判断zhuji是不是软链接
os.path.isdir('/etc')
os.path.exists('/tmp')  # 判断是否存在
os.path.basename('/tmp/abc/aaa.txt')
os.path.dirname('/tmp/abc/aaa.txt')
os.path.split('/tmp/abc/aaa.txt')
os.path.join('/home/tom', 'xyz.txt')
os.path.abspath('test.txt')  # 返回当前目录test.txt的绝对路径

58-pickle存储器
import pickle
“””以前的文件写入，只能写入字符串，如果希望把任意数据对象(数字、列表等)写入文件，
取出来的时候数据类型不变，就用到pickle了
“””

# shop_list = ["eggs", "apple", "peach"]
# with open('/tmp/shop.data', 'wb') as fobj:
#     pickle.dump(shop_list, fobj)

with open('/tmp/shop.data', 'rb') as fobj:
    mylist = pickle.load(fobj)

print(mylist[0], mylist[1], mylist[2])

59-异常处理基础
try: # 把有可能发生异常的语句放到try里执行
n = int(input(“number: “))
result = 100 / n
print(result)
except ValueError:
print(‘invalid number’)
except ZeroDivisionError:
print(‘0 not allowed’)
except KeyboardInterrupt:
print(‘Bye-bye’)
except EOFError:
print(‘Bye-bye’)

print('Done')

60-异常处理完整语法
try:
n = int(input(“number: “))
result = 100 / n
except (ValueError, ZeroDivisionError):
print(‘invalid number’)
except (KeyboardInterrupt, EOFError):
print(‘\nBye-bye’)
else:
print(result) # 异常不发生时才执行else子句
finally:
print(‘Done’) # 不管异常是否发生都必须执行的语句

# 常用形式有try-except和try-finally

21.使用枚举
以下方法将字典作为输入，然后仅返回该字典中的键。

list = [“a”, “b”, “c”, “d”]
for index, element in enumerate(list):
print(“Value”, element, “Index “, index, )

(‘Value’, ‘a’, ‘Index ‘, 0)

(‘Value’, ‘b’, ‘Index ‘, 1)

#(‘Value’, ‘c’, ‘Index ‘, 2)

(‘Value’, ‘d’, ‘Index ‘, 3)

22.计算所需时间
以下代码段可用于计算执行特定代码所需的时间。

import time
start_time = time.time()
a = 1
b = 2
c = a + b
print(c) #3
end_time = time.time()
total_time = end_time - start_time
print(“Time: “, total_time)

(‘Time: ‘, 1.1205673217773438e-05)

23.Try else 指令
你可以将 else 子句作为 try/except 块的一部分，如果没有抛出异常，则执行该子句。

try:
2*3
except TypeError:
print(“An exception was raised”)
else:
print(“Thank God, no exceptions were raised.”)
#Thank God, no exceptions were raised.
24.查找最常见元素
以下方法返回列表中出现的最常见元素。

def most_frequent(list):
return max(set(list), key = list.count)

list = [1,2,1,2,3,2,1,4,2]
most_frequent(list)
25.回文
以下方法可检查给定的字符串是否为回文结构。该方法首先将字符串转换为小写，然后从中删除非字母数字字符。最后，它会将新的字符串与反转版本进行比较。

def palindrome(string):
from re import sub
s = sub(‘[W_]’, ‘’, string.lower())
return s == s[::-1]
palindrome(‘taco cat’) # True
26.没有 if-else 语句的简单计算器
以下代码段将展示如何编写一个不使用 if-else 条件的简单计算器。

import operator
action = {
“+”: operator.add,
“-“: operator.sub,
“/“: operator.truediv,
“*”: operator.mul,
“**”: pow
}
print(action[‘-‘](50, 25)) # 25
27.元素顺序打乱
以下算法通过实现 Fisher-Yates算法 在新列表中进行排序来将列表中的元素顺序随机打乱。

from copy import deepcopy
from random import randint
def shuffle(lst):
temp_lst = deepcopy(lst)
m = len(temp_lst)
while (m):
m -= 1
i = randint(0, m)
temp_lst[m], temp_lst[i] = temp_lst[i], temp_lst[m]
return temp_lst

foo = [1,2,3]
shuffle(foo) # [2,3,1] , foo = [1,2,3]
28.列表扁平化
以下方法可使列表扁平化，类似于JavaScript中的[].concat(…arr)。

def spread(arg):
ret = []
for i in arg:
if isinstance(i, list):
ret.extend(i)
else:
ret.append(i)
return ret
spread([1,2,3,[4,5,6],[7],8,9]) # [1,2,3,4,5,6,7,8,9]
29.变量交换
以下是交换两个变量的快速方法，而且无需使用额外的变量。

def swap(a, b):
return b, a
a, b = -1, 14
swap(a, b) # (14, -1)
30.获取缺失键的默认值
以下代码段显示了如何在字典中没有包含要查找的键的情况下获得默认值。

d = {‘a’: 1, ‘b’: 2}
print(d.get(‘c’, 3)) # 3