The document provides an overview of several Python standard library modules for working with dates, times, files, directories, and system-related tasks. It describes the time and datetime modules for manipulating dates and times. The os, glob, shutil, and tempfile modules are covered for performing file system operations like opening, reading, writing, copying, and deleting files and directories. The sys module is also summarized for working with command line arguments, modules, and standard input/output streams.

1. THE PYTHON STD LIB BY EXAMPLE
– PART 4: DATE,TIME AND SYSTEM
RELATED MODULES
John
Saturday, December 21, 2013

2. DATES AND TIMES

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. Function time – clock time
• Function time return the number of seconds
since the start of epoch
• Function ctime show human-readable
format.

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. Datetime module: doing time and
date parsing
• Class datetime.time: has attribute
hour,minute,second and microsecond and
tzinfo(time zone information)

7. • Class datetime.date: have attribute year,
month and day.
• It is easy to create current date using
function today() method.

8. THE FILE SYSTEM

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. 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. 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. Work with directory - cont
• removedirs,makedirs:
remove and create directory hierarchies.
Instead, rmdir and mkdir only handle single
directory level.

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. 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. 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. 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. 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. 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. 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. 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. Use TemporaryFile create temp
file
>>> import tempfile

22. Another example
• Write something into temp file.
• Use seek() back to the beginning of file. Then
read it

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. 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. 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. 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. THE SYS MODULE

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. 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. Working with modules
• path: The path list contains a list of directory
names where Python looks for extension
modules
import sys
sys.path

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. 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. 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"