????? 6. ??? ????? Python ??? ???8. ???????

?????

• 7.1 ?????????

• 7.2 ??д???

  • 7.2.1 ???????file object??????

  • 7.2.2 pickle ???

 
7. ????????

?м?????????????????????????????????????????????????д????????????á?????????????????е???????

 
7.1 ?????????

??????????????????????????????????print???????????????????????????wite()???????????????????ο?sys.stdout?????????μ???ο??????

??????????????????????Щ????????????????????????????????????????????????????????????????????????????????????????????????????????κ?????????????????????? string ???????Щ????????????????????????????Щ?????????á??????????????????????????????????? % ?????????????????????????????? % ???????????????????????? sprintf()??????????????????????????????ò????з????????????????

??????????????????ν????????????????????????????Python?????????????? repr() ?? str() ??????????????????????????''???????repr???????????????????á?

????str() ???????????????????????????? repr()???????????????????????????е????????????SyntaxError ???? ??????????????????????????????str()??????repr()????????????????????????????????????????????????????????????????????????????????????????????????

???????Щ?????

>>> s = 'Hello, world.'
>>> str(s)
'Hello, world.'
>>> repr(s)
"'Hello, world.'"
>>> str(0.1)
'0.1'
>>> repr(0.1)
'0.10000000000000001'
>>> x = 10 * 3.25
>>> y = 200 * 200
>>> s = 'The value of x is ' + repr(x) + ', and y is ' + repr(y) + '...'
>>> print s
The value of x is 32.5, and y is 40000...
>>> # 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', 'eggs')))
"(32.5, 40000, ('spam', 'eggs'))"
>>> # reverse quotes are convenient in interactive sessions:
... `x, y, ('spam', 'eggs')`
"(32.5, 40000, ('spam', 'eggs'))"

??????????????????????????????

>>> import string
>>> for x in range(1, 11):
...     print string.rjust(repr(x), 2), string.rjust(repr(x*x), 3),
...     # Note trailing comma on previous line
...     print string.rjust(repr(x*x*x), 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(1,11):
...     print '%2d %3d %4d' % (x, x*x, x*x*x)
... 
 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

??????????????print????????????????????????????????????????????

?????????string.rjust()????????????????????????????????У?????????????????????????????????????? string.ljust() ?? string.center()????Щ???????????μ??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????磺"string.ljust(x, n)[0:n]"????

?????????????string.zfill()???????????????????????????0???ú????????????????????

>>> import string
>>> string.zfill('12', 5)
'00012'
>>> string.zfill('-3.14', 7)
'-003.14'
>>> string.zfill('3.14159265359', 5)
'3.14159265359'

??????????????? % ????????

>>> import math
>>> print 'The value of PI is approximately %5.3f.' % math.pi
The value of PI is approximately 3.142.

????г??????????????????????壬?????????????????????????????????????

>>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 7678}

>>> for name, phone in table.items():
...     print '%-10s ==> %10d' % (name, phone)
... 
Jack       ==>       4098
Dcab       ==>       7678
Sjoerd     ==>       4127

???????C????????????????????????????????????????ж??????????????????????????????????????however, if you don't you get an exception, not a core dump?? ??? %s ??????????Щ???????????????????????????????????? str() ???????????????Python????? * ????????????????????????????????Python?????C?? %n ?? %p ????????

??????????????????????????????????????????????????????????????????????????Ч???????????? form %(name)????????

>>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 8637678}
>>> print 'Jack: %(Jack)d; Sjoerd: %(Sjoerd)d; Dcab: %(Dcab)d' % table
Jack: 4098; Sjoerd: 4127; Dcab: 8637678

????????????μ????ú??? vars() ????????????????ú?????????????????о???????????

 
7.2 ??д???

open()  ?????????????? ????????÷??????????????“open(filename, mode)”??

>>> f=open('/tmp/workfile', 'w')
>>> print f
<open file '/tmp/workfile', mode 'w' at 80a0960>

?????????????????????????????????????????????????????????????????????????????????á?????????У?‘r'????????????????‘w’????????????д???????????????ò??????????????????? ‘a’?????????????????????‘r+’??????????д?????????????????????????‘r’????

??Windows ?? Macintosh?????‘b’??????????????????????????????????‘rb’??‘wb’??‘r+b’????????? Windows????????????????????????????????д???????????β?????????н??????? ?????????????????????????????????????JPEG??EXE?????????????????????????????????Щ???????????????????????????????????Mactiontosh????????????????????????C????

 
7.2.1 ???????file object???????

?????е????????????????f?????????

??????????????????? f.read(size)???÷??????????????????????????????????????????????????????size????????С???????????size?????????????????????????????????????????С????????????????????????????????????￡???size???????????????????????????????β??f.read() ????????????????""????

>>> f.read()
'This is the entire file.\n'
>>> f.read()
''

f.readline() ??????ж????????У????????β???????????????з?????е?????????????????з???β???????????????????????????????????????????壬??? if f.readline() ???????????????????????????????β?????????????У?????????‘\n’?????????????з??????????

>>> f.readline()
'This is the first line of the file.\n'
>>> f.readline()
'Second line of the file\n'
>>> f.readline()
''

f.readlines() ????????б?????а?????????????е??????С?????????? sizehint ?????????????????е???????????з??????б?????????????????Ч??????????????????????????????????檔???????????????????С?

>>> f.readlines()
['This is the first line of the file.\n', 'Second line of the file\n']

f.write(string) ?? string ??????д???????????None??

>>> f.write('This is a test\n')

f.tell() ??????????????????????????????е????λ???????????????????????????????????????????????????????????“f.seek(offset, from_what)” ???????ò????д??????????λ????? offset ?????????λ???? from_what ?????????. from_what ??0??????????????????1?????????????λ??????2?????????β????? from_what ???????????????????????????????

>>> f=open('/tmp/workfile', 'r+')
>>> f.write('0123456789abcdef')
>>> f.seek(5)     # Go to the 6th byte in the file
>>> f.read(1)        
'5'
>>> f.seek(-3, 2) # Go to the 3rd byte before the end
>>> f.read(1)
'd'

????????????? f.close() ??????????????????????????????????? f.close()???????????????????????????

>>> f.close()
>>> f.read()
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
ValueError: I/O operation on closed file

??????????Щ???????????????????? isatty() ?? truncate() ???ο????????????????????????

 
7.2.2 pickle ???

??????????????д????е???????????????????????????read() ??????????????????y?????string.atoi()?????У???????'123' ????????????????????????????????????????????????????????????????????????????????????????

????????????????????д???????渴??????????????Python?????????? Pickle ??????顣??????????????????飬??????????κ?Python???????????ЩPython????饗form??????????????????????????????? ??pickling??????????????????1??????????????unpickling??????????е???????洢???????????У???????????????????????????

??????????????x???????д?????????????f????????????????????????д???

pickle.dump(x, f)

???f???????????????????????????????????????

x = pickle.load(f)

??????????????????д??????????????Щ??????仯???á???????pickle????????ο??????

pickle ??洢Python?????????????????????????????????????????鼼????????????????? persistent object ??????? pickle ?????????????Python???????????????????????????????????????????????????

????? 6. ??? ????? Python ??? ???8. ???????

Release 2.3, documentation updated on July 29, 2003.