7. Input and Output

'Hello,world,'
repr(s)
"'Hello,world,'"
str(1/7)
'0.14285714285714285'
x = 10 * 3.25
y = 200 * 2000
s = 'The value of x is ' + repr(x) + ', and y is' + repr(y) +'...' 
print(s)
The value of x is 32.5, and y is400000...
# The repr() of a string adds string quotes and backslashes:
hello = 'hello, world\n'
hellos =  repr(hello)
print(hellos)
'hello, world\n'
# The argument to repr() may be any Python object：
repr((x,y,('spam','egges')))
"(32.5, 400000, ('spam', 'egges'))"

for x in range(1, 11):
    print(repr(x).rjust(2),repr(x*x).rjust(3),end=' ')
    # Note use of 'and' on previous line
    print(repr(x*x*x).rjust(4))
    
 1   1    1
 2   4    8
 3   9   27
 4  16   64
 5  25  125
 6  36  216
 7  49  343
 8  64  512
 9  81  729
10 100 1000
for x in range(2,22):
    print('{0:2d} {1:3d}  {2:4d}'.format(x,x*x,x*x*x))
    
 2   4     8
 3   9    27
 4  16    64
 5  25   125
 6  36   216
 7  49   343
 8  64   512
 9  81   729
10 100  1000
11 121  1331
12 144  1728
13 169  2197
14 196  2744
15 225  3375
16 256  4096
17 289  4913
18 324  5832
19 361  6859
20 400  8000
21 441  9261

菜鸟教程网址： "www.runoob.com!"
print('{0}和{1}'.format('Google','Runoob'))
Google和Runoob
print('{1}和{0}'.format('Google','Runoob'))
Runoob和Google
print('{name}网址： {site}'.format(name='菜鸟教程',site='www.henrytien.com'))
菜鸟教程网址： www.henrytien.com
print('站点列表 {0},{1},和{other}.'.format('Google','Runoob',other='Taobao'))
站点列表 Google,Runoob,和Taobao.

print('My hovercraft is full of {}.'.format(conttens))
My hovercraft is full of eels.
print('My hovercraft if full of {!r}.'.format(conttens))
My hovercraft if full of 'eels'.

print('The value ofPI is approximately {0:.3f}.'.format(math.pi))
The value ofPI is approximately 3.142.

table = {'Google':1,'Runoob':2,'Taobao':3}
for name, number in table.items():
    print('{0:10} ==> {1:10d}'.format(name,number))
    
Google     ==>          1
Runoob     ==>          2
Taobao     ==>          3

7.2 Reading and Writing Files

f = open("C:/Users\henry\desktop/foo.txt",'rb+')
f.write(b'lsldllsas')
9
f.seek(5)
5
f.read(1)
b'l'
f.seek(-3,2)
27
f.read(1)
b'1'

7.2.2. Saving strucured data with json

import json
json.dumps([1,'simple','list'])
'[1, "simple", "list"]'
json.dump(x,f)