THE PYTHON STD LIB BY EXAMPLE – PART 4: DATE,TIME AND SYSTEM

RELATED MODULES

JohnSunday, April 9, 2023

DATES AND TIMES

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.

Function time – clock time

• Function time return the number of seconds since the start of epoch

• Function ctime show human-readable format.

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)

Datetime module: doing time and date parsing• Class datetime.time: has attribute

hour,minute,second and microsecond and tzinfo(time zone information)

• Class datetime.date: have attribute year, month and day.

• It is easy to create current date using function today() method.

THE FILE SYSTEM

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

Work with file• open:create, open, and modify files• remove: delete filesCode Example:

import osfi = open(file)fo = open(temp,”w”) #w mean write permissonfor s in fi.readlines():

fo.write(s)fi.closefo.closeos.remove(back)

Work with directory

• listdir,chdir,mkdir,rmdir,getcwd: Please guess the function by the name

import osos.getpwd() # get the current diros.chdir(‘..’) # change to the parent directory

os.getcwd()os.listdir(‘.’) #list the file under the diros.mkdir(‘./temp1’) #make new dir

os.rmdir(‘./temp1’) #delete the diros.listdir(‘.’) # check if the delete is successful

Work with directory - cont

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

Work with file attributes

• stat: It returns a 9-tuple which contains thesize, inode change timestamp, modification timestamp, and access privileges of a file. Similar as unix stat.

import osfile = "samples/sample.jpg“

st = os.stat(file)size = st[6] #file size

Working with processes

• system:runs a new command under the current process, and waits for it to finish

import osos.system('dir')os.system('notepad') # open notepad

The os.path class• This module contains functions that deal with long filenames (path

names) in various ways. • Learn from example

import osfilename = "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))

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

os.environ

• A mapping object representing the string environment. => key value pairs

a = os.environdir(a) # show all the functions of a a.keys() #show all the keysa.has_key('USERNAME') #check if has this keyprint a['USERNAME‘] # return the value of this key

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

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]

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.

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.– 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

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

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.

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

THE SYS MODULE

Brief introduction

• This module provides access to some variables used or maintained by the interpreter and to functions that interact strongly with the interpreter.

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.pyimport sysprint "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”

Working with modules

• path: The path list contains a list of directory names where Python looks for extension modules

import syssys.path

sys.platform

• The platform variable contains the name of the host platform

import syssys.platform

• Typical platform names are win32 for Windows

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.stdoutf = open(‘file1.txt’,’w’)Sys.stdout = f #change the stdout to file1.txtprint “hello,world” sys.stdout = saveout

In this example, “hello,world” string has written to file1.txt.

sys.exit:Exiting the program

• This function takes an optional integer value, which is returned to the calling program.

import sysprint "hello"sys.exit(1)print "there"