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THE PYTHON STD LIB BY EXAMPLE
– PART 4: DATE,TIME AND SYSTEM
RELATED MODULES
John
Saturday, December 21, 2013
DATES AND TIMES
Brief introduction
• The time module includes clock time and the
processor run-time
• The datetime module provide a higher...
Function time – clock time
• Function time return the number of seconds
since the start of epoch
• Function ctime show hum...
Function clock – processor clock
time
• Use it for perfomance testing, beachmarking.
• function time.clock()
>>>import tim...
Datetime module: doing time and
date parsing
• Class datetime.time: has attribute
hour,minute,second and microsecond and
t...
• Class datetime.date: have attribute year,
month and day.
• It is easy to create current date using
function today() meth...
THE FILE SYSTEM
Brief introduction
• Standard library includes a large range of
tools working with files.
• The os module provides a way r...
Work with file
• open:create, open, and modify files
• remove: delete files
Code Example:
import os
fi = open(file)
fo = o...
Work with directory
• listdir,chdir,mkdir,rmdir,getcwd: Please
guess the function by the name
import os
os.getpwd() # get ...
Work with directory - cont
• removedirs,makedirs:
remove and create directory hierarchies.
Instead, rmdir and mkdir only h...
Work with file attributes
• stat: It returns a 9-tuple which contains the
size, inode change timestamp, modification
times...
Working with processes
• system:runs a new command under the
current process, and waits for it to finish
import os
os.syst...
The os.path class
• This module contains functions that deal with long filenames (path
names) in various ways.
• Learn fro...
Using the os.path module to check
what a filename represents
• Learn from example
for file in FILES:
print file, "=>",
if ...
os.environ
• A mapping object representing the string
environment. => key value pairs
a = os.environ
dir(a) # show all the...
The glob module: search dir
• An asterisk(*) mathes 0 or more characters in
a segment of a name
>>> import glob
>>> for na...
More wildcards in glob
• A question mark (?) matches any single
character
>>> for name in glob.glob(‘./file?.txt’):
print ...
The tempfile module: Temporary
file system object
• Application need temporary file to store
data.
• This module create te...
Use TemporaryFile create temp
file
>>> import tempfile
Another example
• Write something into temp file.
• Use seek() back to the beginning of file. Then
read it
More methods in tempfile
• Method NamedTemporaryFile()
– Similar as TemporaryFile but it give a named
temporrary file.
– L...
Module shutil – high level file
operation
• Method copyfile(source,destination): copy
source file to destination)

• Metho...
More functions in shutil
• Method copytree(dir1, dir2): copy a dir1 to
dir2
• Method rmtree(dir): remove a dir and its
con...
Module filecmp: compare files
and dir
• Function filecmp.cmp(file1,file2): return True
or False
• Function filecmp.dircmp(...
THE SYS MODULE
Brief introduction
• This module provides access to some
variables used or maintained by the
interpreter and to functions ...
Working with command-line arguments
• argv list contain the arguments passed to the script.
The first is the script itself...
Working with modules
• path: The path list contains a list of directory
names where Python looks for extension
modules

im...
sys.platform
• The platform variable contains the name of
the host platform
import sys
sys.platform

• Typical platform na...
Working with standard input and output
• The stdin, stdout and stderr variables contain
stream objects corresponding to th...
sys.exit:Exiting the program
• This function takes an optional integer value,
which is returned to the calling program.
im...
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Python advanced 3.the python std lib by example – system related modules

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Transcript of "Python advanced 3.the python std lib by example – system related modules"

  1. 1. THE PYTHON STD LIB BY EXAMPLE – PART 4: DATE,TIME AND SYSTEM RELATED MODULES John Saturday, December 21, 2013
  2. 2. DATES AND TIMES
  3. 3. Brief introduction • The time module includes clock time and the processor run-time • The datetime module provide a higher-level interface for date, time and combined values. It support arithmetic,comparison, and time zone configuration. • The calendar module includeweeks,months, and years.
  4. 4. Function time – clock time • Function time return the number of seconds since the start of epoch • Function ctime show human-readable format.
  5. 5. Function clock – processor clock time • Use it for perfomance testing, beachmarking. • function time.clock() >>>import time >>>for i in range(6,1,-1): print '%s %0.2f %0.2f' % (time.ctime(),time.time(),time.clock()) print 'sleeping', i time.sleep(i)
  6. 6. Datetime module: doing time and date parsing • Class datetime.time: has attribute hour,minute,second and microsecond and tzinfo(time zone information)
  7. 7. • Class datetime.date: have attribute year, month and day. • It is easy to create current date using function today() method.
  8. 8. THE FILE SYSTEM
  9. 9. Brief introduction • Standard library includes a large range of tools working with files. • The os module provides a way regardless the operation systems. • The glob module help scan the directory contents
  10. 10. Work with file • open:create, open, and modify files • remove: delete files Code Example: import os fi = open(file) fo = open(temp,”w”) #w mean write permisson for s in fi.readlines(): fo.write(s) fi.close fo.close os.remove(back)
  11. 11. Work with directory • listdir,chdir,mkdir,rmdir,getcwd: Please guess the function by the name import os os.getpwd() # get the current dir os.chdir(‘..’) # change to the parent directory os.getcwd() os.listdir(‘.’) #list the file under the dir os.mkdir(‘./temp1’) #make new dir os.rmdir(‘./temp1’) #delete the dir os.listdir(‘.’) # check if the delete is successful
  12. 12. Work with directory - cont • removedirs,makedirs: remove and create directory hierarchies. Instead, rmdir and mkdir only handle single directory level.
  13. 13. Work with file attributes • stat: It returns a 9-tuple which contains the size, inode change timestamp, modification timestamp, and access privileges of a file. Similar as unix stat. import os file = "samples/sample.jpg“ st = os.stat(file) size = st[6] #file size
  14. 14. Working with processes • system:runs a new command under the current process, and waits for it to finish import os os.system('dir') os.system('notepad') # open notepad
  15. 15. The os.path class • This module contains functions that deal with long filenames (path names) in various ways. • Learn from example import os filename = "my/little/pony" print "using", os.name, "..." print "split", "=>", os.path.split(filename) print "splitext", "=>", os.path.splitext(filename) print "dirname", "=>", os.path.dirname(filename) print "basename", "=>", os.path.basename(filename) print "join", "=>", os.path.join(os.path.dirname(filename), os.path.basename(filename))
  16. 16. Using the os.path module to check what a filename represents • Learn from example for file in FILES: print file, "=>", if os.path.exists(file): print "EXISTS", if os.path.isabs(file): print "ISABS", if os.path.isdir(file): print "ISDIR", if os.path.isfile(file): print "ISFILE", if os.path.islink(file): print "ISLINK", if os.path.ismount(file): print "ISMOUNT", print
  17. 17. os.environ • A mapping object representing the string environment. => key value pairs a = os.environ dir(a) # show all the functions of a a.keys() #show all the keys a.has_key('USERNAME') #check if has this key print a['USERNAME‘] # return the value of this key
  18. 18. The glob module: search dir • An asterisk(*) mathes 0 or more characters in a segment of a name >>> import glob >>> for name in glob.glob(‘dir/*’) print name
  19. 19. More wildcards in glob • A question mark (?) matches any single character >>> for name in glob.glob(‘./file?.txt’): print name ./file1.txt ./file2.txt • Others: character range e.g. [a-z], [0-9]
  20. 20. The tempfile module: Temporary file system object • Application need temporary file to store data. • This module create temporary files with unique names securely. • The file is removed automatically when it is closed.
  21. 21. Use TemporaryFile create temp file >>> import tempfile
  22. 22. Another example • Write something into temp file. • Use seek() back to the beginning of file. Then read it
  23. 23. More methods in tempfile • Method NamedTemporaryFile() – Similar as TemporaryFile but it give a named temporrary file. – Leave it to user fig out (Follow the example of TemporaryFile). • Method mkdtemp(): create temp dir • Method gettempdir(): return the default dir store temp file
  24. 24. Module shutil – high level file operation • Method copyfile(source,destination): copy source file to destination) • Method copy(source file, dir): copy the file under the dir
  25. 25. More functions in shutil • Method copytree(dir1, dir2): copy a dir1 to dir2 • Method rmtree(dir): remove a dir and its contents. • Method move(source,destination): move a file or dir from one place to another.
  26. 26. Module filecmp: compare files and dir • Function filecmp.cmp(file1,file2): return True or False • Function filecmp.dircmp(dir1,dir2).report(): output a plain-text report
  27. 27. THE SYS MODULE
  28. 28. Brief introduction • This module provides access to some variables used or maintained by the interpreter and to functions that interact strongly with the interpreter.
  29. 29. Working with command-line arguments • argv list contain the arguments passed to the script. The first is the script itself (sys.argv[0]) # File:sys-argv-example-1.py import sys print "script name is", sys.argv[0] for arg in sys.argv[1:]: print arg • Save the code to file sys-argv-example-1.py, run command line “python sys-argv-example-1.py –c option1 –d option2”
  30. 30. Working with modules • path: The path list contains a list of directory names where Python looks for extension modules import sys sys.path
  31. 31. sys.platform • The platform variable contains the name of the host platform import sys sys.platform • Typical platform names are win32 for Windows
  32. 32. Working with standard input and output • The stdin, stdout and stderr variables contain stream objects corresponding to the standard I/O streams. #File “test.py” saveout = sys.stdout f = open(‘file1.txt’,’w’) Sys.stdout = f #change the stdout to file1.txt print “hello,world” sys.stdout = saveout In this example, “hello,world” string has written to file1.txt.
  33. 33. sys.exit:Exiting the program • This function takes an optional integer value, which is returned to the calling program. import sys print "hello" sys.exit(1) print "there"
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