python lession 4 -- IO --

• str() repr()

>>> s = 'Hello, world.'
>>> str(s)
'Hello, world.'
>>> repr(s)
"'Hello, world.'"
>>> str(1.0/7.0)
'0.142857142857'
>>> repr(1.0/7.0)
'0.14285714285714285'

 write a table

>>> for x in range(1,11):
...     print repr(x).rjust(2),
...     print repr(x*x).rjust(3),
...     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

write a table 2.0

 1 >>> for x in range(1,11):
 2 ...     print '{0:2d} {1:3d} {2:4d}'.format(x, x*x, x*x*x)
 3 ...
 4  1   1    1
 5  2   4    8
 6  3   9   27
 7  4  16   64
 8  5  25  125
 9  6  36  216
10  7  49  343
11  8  64  512
12  9  81  729
13 10 100 1000

zfill

>>> 'hello'.zfill(10)
'00000hello'
>>> '12.3'.zfill(7)
'00012.3'

str.format()

>>> print "hello {}".format("york")
hello york

>>> print "{1} {0}!".format("york","hello")
hello york!

>>> print "{greeting} {people}".format(greeting="good morning",people="york")
good morning york

'!r'

>>> import math
>>> print 'The value of PI is approximately {}.'.format(math.pi)
The value of PI is approximately 3.14159265359.
>>> print 'The value of PI is approximately {!r}.'.format(math.pi)
The value of PI is approximately 3.141592653589793.

>>> import math
>>> print 'The value of PI is approximately {0:.3f}.'.format(math.pi)
The value of PI is approximately 3.142.

>>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 7678}
>>> for name, phone in table.items():
...     print '{0:10} ==> {1:10d}'.format(name, phone)
...
Jack       ==>       4098
Dcab       ==>       7678
Sjoerd     ==>       4127

Open files

open(filename, mode)
'r' only be read,
'w'  only writing,
'a' for appending,
'r+' both reading and writing,
'r' will be assumed if it’s omitted.

file:read() f.read(size), size is optional, return string.caution!: it’s your problem if the file is twice as large as your machine’s memory

>>> f = open("hello.txt")
>>> f.read()
'hello world!\nsecond line!\nthird line!\n'

file:readline() 

>>> f = open("hello.txt")
>>> f.readline()
'hello world!\n'
>>> f.readline()
'second line!\n'
>>> f.readline()
'third line!\n'
>>> f.readline()
''
>>> f.readline()
''

f.readlines()

>>> f.readlines()
['hello world!\n', 'second line!\n', 'third line!\n']

another way to process each line in the file

>>> f = open("hello.txt")
>>> for line in f:
...     print line
... 
hello world!

second line!

third line!

f.write()

>>> f = open("hello.txt","a")
>>> f.write("this is forth lien\n")

f.tell(), f.seek(position)

>>> f.seek(0)
>>> f.read(1)
'h'
>>> f.tell()
1L

Pickle:read/write some abstract object

pickle.dump(x, f)

x = pickle.load(f)

转载于:https://www.cnblogs.com/chhyong88/archive/2012/02/06/2340432.html