cities = ['Shanghai','beijing','Chengdu']
i = 0
for c in cities:
    print(i +1,'-->',c)
    i += 1

cities = ['Shanghai','beijing','Chengdu']
for i,city in enumerate(cities):
    print(i+1,'-->',city)

names = ['leo','jack','james']
colors = ['red','green','blue','yellow']
n = min(len(names),len(colors))
for i in range(n):
    print(names[i],'-->',colors[i])

names = ['leo','jack','james']
colors = ['red','green','blue','yellow']
for name,color in zip(names,colors):
    print(name,'-->',color)

x = 1
y = 2
print('>>Before:x={},y={}'.format(x,y))
tmp = y
y = x
x = tmp
print('>>After:x = {},y = {}'.format(x,y))

x = 1
y= 2
print('Before:x = {},y = {}'.format(x,y))
x,y = y,x
print('After:x = {},y = {}'.format(x,y))

students = {'Lili':18,'Sam':25}
if 'Susan' in students:
    student = students['Susan']
else:
    student = 'unknow'
print('Susan is {} yesrs old'.format(student))

students = {'Lili':18,'San':25}
student = students.get('Susan','unknow')
print('Susan is {} yesrs'.format(student))

target_letter = 'd'
letters = ['a','b','c']

found = False
for letter in letters:
    if letter == target_letter:
        print('Found')
        found = True
        break
if not found:
    print('Not Found')

target_letter = 'd'
letters = ['a','b','c']

for letter in letters:
    if letter == target_letter:
        print('found')
        break
else:
    print('Not Found')

f = open('data.txt')
try:
    text = f.read()
    for line in text.split('\n'):
        print(line)
finally:
    f.close()

with open('data.txt') as f:
    for line in f:
        print(line.strip('\n'))

import threading

lock = threading.Lock()
lock.acquire()
try:
    print('Citical par,do somethins...')
finally:
    lock.release()

import threading
lock = threading.Lock()
with lock:
    print('Citical par,do somethins...')