最基本的文件操作当然就是在文件中读写数据。这也是很容易掌握的。现在打开一个文件以进行写操作:1. fileHandle = open ( ‘test.txt’, ‘w’ )fileHandle = open ( ‘test.txt’, ‘w’ )
‘w’是指文件将被写入数据,语句的其它部分很好理解。下一步就是将数据写入文件:
1. fileHandle.write ( ‘This is a test.\nReally, it is.’ )
fileHandle.write ( ‘This is a test.\nReally, it is.’ )
这个语句将“This is a test.”写入文件的第一行,“Really, it is.”写入文件的第二行。最后,我们需要做清理工作,并且关闭文件:
1. fileHandle.close()
fileHandle.close()
正如你所见,在Python的面向对象机制下,这确实非常简单。需要注意的是,当你再次使用“w”方式在文件中写数据,所有原来的内容都会被删除。如果想保留原来的内容,可以使用“a”方式在文件中结尾附加数据:
1. fileHandle = open ( ‘test.txt’, ‘a’ )2. fileHandle.write ( ‘\n\nBottom line.’ )3. fileHandle.close()
fileHandle = open ( ‘test.txt’, ‘a’ )fileHandle.write ( ‘\n\nBottom line.’ )fileHandle.close()
然后,我们读取test.txt,并将内容显示出来:
1. fileHandle = open ( ‘test.txt’ )2. print fileHandle.read()3. fileHandle.close()
fileHandle = open ( ‘test.txt’ )print fileHandle.read()fileHandle.close()
以上语句将读取整个文件并显示其中的数据。我们也可以读取文件中的一行:
1. fileHandle = open ( ‘test.txt’ )2. print fileHandle.readline() # “This is a test.”3. fileHandle.close()
fileHandle = open ( ‘test.txt’ )print fileHandle.readline() # “This is a test.”fileHandle.close()
同时,也可以将文件内容保存到一个list中:
1. fileHandle = open ( ‘test.txt’ )2. fileList = fileHandle.readlines()<div></div>3. for fileLine in fileList:4.???? print ‘>>’, fileLine5. fileHandle.close()
fileHandle = open ( ‘test.txt’ )fileList = fileHandle.readlines()for fileLine in fileList:print ‘>>’, fileLinefileHandle.close()
Python在读取一个文件时,会记住其在文件中的位置,如下所示:
1. fileHandle = open ( ‘test.txt’ )2. garbage = fileHandle.readline()3. fileHandle.readline() # “Really, it is.”fileHandle.close()
fileHandle = open ( ‘test.txt’ )garbage = fileHandle.readline()fileHandle.readline() # “Really, it is.”fileHandle.close()
可以看到,只有第二行显示出来。然而,我们可以让Python从头开始读来解决这个问题:
1. fileHandle = open ( ‘test.txt’ )2. garbage = fileHandle.readline()3. fileHandle.seek ( 0 )4. print fileHandle.readline() # “This is a test.”5. fileHandle.close()
fileHandle = open ( ‘test.txt’ )garbage = fileHandle.readline()fileHandle.seek ( 0 )print fileHandle.readline() # “This is a test.”fileHandle.close()
在上面这个例子中,我们让Python从文件第一个字节开始读取数据。所以,第一行文字显示了出来。当然,我们也可以获取Python在文件中的位置:
1. fileHandle = open ( ‘test.txt’ )2. print fileHandle.readline() # “This is a test.”3. print fileHandle.tell() # “17″4. print fileHandle.readline() # “Really, it is.”
fileHandle = open ( ‘test.txt’ )print fileHandle.readline() # “This is a test.”print fileHandle.tell() # “17″print fileHandle.readline() # “Really, it is.”
或者在文件中一次读取几个字节的内容:
1. fileHandle = open ( ‘test.txt’ )2. print fileHandle.read ( 1 ) # “T”3. fileHandle.seek ( 4 )4. print FileHandle.read ( 1 ) # ” “(原文有错)
fileHandle = open ( ‘test.txt’ )print fileHandle.read ( 1 ) # “T”fileHandle.seek ( 4 )print FileHandle.read ( 1 ) # ” “(原文有错)
在Windows和Macintosh环境下,有时可能需要以二进制方式读写文件,比如图片和可执行文件。此时,只要在打开文件的方式参数中增加一个“b”即可:
1. fileHandle = open ( ‘testBinary.txt’, ‘wb’ )2. fileHandle.write ( ‘There is no spoon.’ )3. fileHandle.close()
fileHandle = open ( ‘testBinary.txt’, ‘wb’ )fileHandle.write ( ‘There is no spoon.’ )fileHandle.close()
1. fileHandle = open ( ‘testBinary.txt’, ‘rb’ )2. print fileHandle.read()3. fileHandle.close()
fileHandle = open ( ‘testBinary.txt’, ‘rb’ )print fileHandle.read()fileHandle.close()
二、从现有文件中获取信息使用Python中的模块,可以从现有文件中获取信息。使用“os”模块和“stat”模块可以获取文件的基本信息:
1. import os2. import stat3. import time<div></div>4.5. fileStats = os.stat ( ‘test.txt’ )6. fileInfo = {7.???? ‘Size’ : fileStats [ stat.ST_SIZE ],8.???? ‘LastModified’ : time.ctime ( fileStats [ stat.ST_MTIME ] ),9.???? ‘LastAccessed’ : time.ctime ( fileStats [ stat.ST_ATIME ] ),10.???? ‘CreationTime’ : time.ctime ( fileStats [ stat.ST_CTIME ] ),11.???? ‘Mode’ : fileStats [ stat.ST_MODE ]12. }13.14. for infoField, infoValue in fileInfo:15.???? print infoField, ‘:’ + infoValue16. if stat.S_ISDIR ( fileStats [ stat.ST_MODE ] ):17.???? print ‘Directory. ‘18. else:19.???? print ‘Non-directory.’
import osimport statimport time
fileStats = os.stat ( ‘test.txt’ )fileInfo = {‘Size’ : fileStats [ stat.ST_SIZE ],‘LastModified’ : time.ctime ( fileStats [ stat.ST_MTIME ] ),‘LastAccessed’ : time.ctime ( fileStats [ stat.ST_ATIME ] ),‘CreationTime’ : time.ctime ( fileStats [ stat.ST_CTIME ] ),‘Mode’ : fileStats [ stat.ST_MODE ]}
for infoField, infoValue in fileInfo:print infoField, ‘:’ + infoValueif stat.S_ISDIR ( fileStats [ stat.ST_MODE ] ):print ‘Directory. ‘else:print ‘Non-directory.’
上面这个例子创建了一个包含文件基本信息的dictionary。然后显示了相关信息,并且告诉我们打开的是否为目录。我们也可以试一下打开的是否是其它几种类型:
1. import os2. import stat3.4. fileStats = os.stat ( ‘test.txt’ )5. fileMode = fileStats [ stat.ST_MODE ]6. if stat.S_ISREG ( fileStats [ stat.ST_MODE ] ):7.???? print ‘Regular file.’8. elif stat.S_ISDIR ( fileStats [ stat.ST_MODE ] ):9.???? print ‘Directory.’10. elif stat.S_ISLNK ( fileStats [ stat.ST_MODE ] ):11.???? print ‘Shortcut.’12. elif stat.S_ISSOCK ( fileStats [ stat.ST_MODE ] ):13.???? print ‘Socket.’14. elif stat.S_ISFIFO ( fileStats [ stat.ST_MODE ] ):15.???? print ‘Named pipe.’16. elif stat.S_ISBLK ( fileStats [ stat.ST_MODE ] ):17.???? print ‘Block special device.’18. elif stat.S_ISCHR ( fileStats [ stat.ST_MODE ] ):19.???? print ‘Character special device.’
import osimport stat
fileStats = os.stat ( ‘test.txt’ )fileMode = fileStats [ stat.ST_MODE ]if stat.S_ISREG ( fileStats [ stat.ST_MODE ] ):print ‘Regular file.’elif stat.S_ISDIR ( fileStats [ stat.ST_MODE ] ):print ‘Directory.’elif stat.S_ISLNK ( fileStats [ stat.ST_MODE ] ):print ‘Shortcut.’elif stat.S_ISSOCK ( fileStats [ stat.ST_MODE ] ):print ‘Socket.’elif stat.S_ISFIFO ( fileStats [ stat.ST_MODE ] ):print ‘Named pipe.’elif stat.S_ISBLK ( fileStats [ stat.ST_MODE ] ):print ‘Block special device.’elif stat.S_ISCHR ( fileStats [ stat.ST_MODE ] ):print ‘Character special device.’
另外,我们可以使用“os.path”来获取基本信息:
1. import os.path2.3. fileStats = ‘test.txt’4. if os.path.isdir ( fileStats ):5.???? print ‘Directory.’6. elif os.path.isfile ( fileStats ):7.???? print ‘File.’8. elif os.path.islink ( fileStats ):9.???? print ‘Shortcut.’10. elif os.path.ismount ( fileStats ):11.???? print ‘Mount point.’
import os.path
fileStats = ‘test.txt’if os.path.isdir ( fileStats ):print ‘Directory.’elif os.path.isfile ( fileStats ):print ‘File.’elif os.path.islink ( fileStats ):print ‘Shortcut.’elif os.path.ismount ( fileStats ):print ‘Mount point.’
三、目录和普通文件一样,关于目录的操作也很容易掌握。首先,列出一个目录的内容:
1. import os2.3. for fileName in os.listdir ( ‘/’ ):4.???? print fileName
import os
for fileName in os.listdir ( ‘/’ ):print fileName
正如你所见,这很简单,用三行代码就可以完成。创建目录也很简单:
1. import os2.3. os.mkdir ( ‘testDirectory’ )
import os
os.mkdir ( ‘testDirectory’ )
删除刚才创建的目录:
1. import os2.3. os.rmdir ( ‘testDirectory )
import os
os.rmdir ( ‘testDirectory )
嗯,可以创建多级目录:
1. import os2.3. os.makedirs ( ‘I/will/show/you/how/deep/the/rabbit/hole/goes’ )
import os
os.makedirs ( ‘I/will/show/you/how/deep/the/rabbit/hole/goes’ )
如果没有在创建的文件夹中添加任何东西,就可以一次性将它们全部删除(即,删除所列的所有空文件夹):
1. import os2.3. os.removedirs ( ‘I/will/show/you/how/deep/the/rabbit/hole/goes’ )
import os
os.removedirs ( ‘I/will/show/you/how/deep/the/rabbit/hole/goes’ )
当需要对一个特定的文件类型进行操作时,我们可以选择“fnmatch”模块。以下是显示“.txt”文件的内容和“.exe”文件的文件名:
1. import fnmatch2. import os3.4. for fileName in os.listdir ( ‘/’ ):5.???? if fnmatch.fnmath ( fileName, ‘*.txt’ ):6.???????? print open ( fileName ).read()7.???? elif fnmatch.fnmatch ( fileName, ‘*.exe’ ):8.???????? print fileName
import fnmatchimport os
for fileName in os.listdir ( ‘/’ ):if fnmatch.fnmath ( fileName, ‘*.txt’ ):print open ( fileName ).read()elif fnmatch.fnmatch ( fileName, ‘*.exe’ ):print fileName
“*”字符可以表示任意长度的字符。如果要匹配一个字符,则使用“?”符号:
1. import fnmatch2. import os3.4. for fileName in os.listdir ( ‘/’ ):5.???? if fnmatch.fnmatch ( fileName, ‘?.txt’ ):6.???????? print ‘Text file.’
import fnmatchimport os
for fileName in os.listdir ( ‘/’ ):if fnmatch.fnmatch ( fileName, ‘?.txt’ ):print ‘Text file.’
“fnmatch”模块支持正则表达式:
1. import fnmatch2. import os3. import re4.5. filePattern = fnmatch.translate ( ‘*.txt’ )6. for fileName in os.listdir ( ‘/’ ):7.???? if re.match ( filePattern, fileName ):8.???????? print ‘Text file.’
import fnmatchimport osimport re
filePattern = fnmatch.translate ( ‘*.txt’ )for fileName in os.listdir ( ‘/’ ):if re.match ( filePattern, fileName ):print ‘Text file.’
若只需要匹配一种类型的文件,更好的办法是使用“glob”模块。该模块的格式和“fnmatch”相似:
1. import glob2.3. for fileName in glob.glob ( ‘*.txt’ ):4.???? print ‘Text file.’
import glob
for fileName in glob.glob ( ‘*.txt’ ):print ‘Text file.’
使用一定范围的字符来匹配同样可行,就像在正则表达式中使用一样。假设你想要显示扩展名前只有一位数字的文件的文件名:
1. import glob2.3. for fileName in glob.glob ( ‘[0-9].txt’ ):4.???? print filename
import glob
for fileName in glob.glob ( ‘[0-9].txt’ ):print filename
“glob”模块利用“fnmatch”模块来实现。
四、数据编组使用前一节中介绍的模块,可以实现在文件中对字符串的读写。然而,有的时候,你可能需要传递其它类型的数据,如list、tuple、dictionary和其它对象。在Python中,你可以使用Pickling来完成。你可以使用Python标准库中的“pickle”模块完成数据编组。下面,我们来编组一个包含字符串和数字的list:
1. import pickle2.3. fileHandle = open ( ‘pickleFile.txt’, ‘w’ )4. testList = [ ‘This’, 2, ‘is’, 1, ‘a’, 0, ‘test.’ ]5. pickle.dump ( testList, fileHandle )6. fileHandle.close()
import pickle
fileHandle = open ( ‘pickleFile.txt’, ‘w’ )testList = [ ‘This’, 2, ‘is’, 1, ‘a’, 0, ‘test.’ ]pickle.dump ( testList, fileHandle )fileHandle.close()
拆分编组同样不难:
1. import pickle2.3. fileHandle = open ( ‘pickleFile.txt’ )4. testList = pickle.load ( fileHandle )5. fileHandle.close()
import pickle
fileHandle = open ( ‘pickleFile.txt’ )testList = pickle.load ( fileHandle )fileHandle.close()
现在试试存储更加复杂的数据:
1. import pickle2.3. fileHandle = open ( ‘pickleFile.txt’, ‘w’ )4. testList = [ 123, { ‘Calories’ : 190 }, ‘Mr. Anderson’, [ 1, 2, 7 ] ]5. pickle.dump ( testList, fileHandle )6. fileHandle.close()
import pickle
fileHandle = open ( ‘pickleFile.txt’, ‘w’ )testList = [ 123, { ‘Calories’ : 190 }, ‘Mr. Anderson’, [ 1, 2, 7 ] ]pickle.dump ( testList, fileHandle )fileHandle.close()
1. import pickle2.3. fileHandle = open ( ‘pickleFile.txt’ )4. testList = pickle.load ( fileHandle )5. fileHandle.close()
import pickle
fileHandle = open ( ‘pickleFile.txt’ )testList = pickle.load ( fileHandle )fileHandle.close()
如上所述,使用Python的“pickle”模块编组确实很简单。众多对象可以通过它来存储到文件中。如果可以的话,“cPickle”同样胜任这个工作。它和“pickle”模块一样,但是速度更快:
1. import cPickle2.3. fileHandle = open ( ‘pickleFile.txt’, ‘w’ )4. cPickle.dump ( 1776, fileHandle )5. fileHandle.close()
import cPickle
fileHandle = open ( ‘pickleFile.txt’, ‘w’ )cPickle.dump ( 1776, fileHandle )fileHandle.close()
五、创建“虚拟”文件你用到的许多模块包含需要文件对象作为参数的方法。但是,有时创建并使用一个真实的文件并让人感到有些麻烦。所幸的是,在Python中,你可以使用“StringIO”模块来创建文件并将其保存在内存中:
1. import StringIO2.3. fileHandle = StringIO.StringIO ( “Let freedom ring” )4. print fileHandle.read() # “Let freedom ring.”5. fileHandle.close()
import StringIO
fileHandle = StringIO.StringIO ( “Let freedom ring” )print fileHandle.read() # “Let freedom ring.”fileHandle.close()
cStringIO”模块同样有效。它的使用方法和“StringIO”一样,但就像“cPickle”之于“pickle”,它速度更快:
1. import cStringIO2.3. fileHandle = cStringIO.cStringIO ( “To Kill a Mockingbird” )4. print fileHandle.read() # “To Kill a Mockingbid”5. fileHandle.close()
import cStringIO
fileHandle = cStringIO.cStringIO ( “To Kill a Mockingbird” )print fileHandle.read() # “To Kill a Mockingbid”fileHandle.close()