Command line arguments stored in sys.argv and get by index sys.argv[0]
comment start with pound(#) sign.
indentation is use for grouping statments like we are using {} in C++ or perl for grouping or making for loops and if conditional statements
compileall tool is use for generate .pyc “byte-compiled” version of the module.
first line of script #! /usr/bin/env python
define source code encoding
# -*- coding: encoding -*-
# -*- coding: iso-8859-15 -*-
setting python startup script by setting an environment variable named PYTHONSTARTUP. this script will run evry time python interpreter start.
command line arguments
len(sys.argv) # number of arguments
sys.argv[0] # script name
looping and condition statements
checking condition use keywords : in, not in, is, is not, and, or
if statment
if x>100:
.....
elif x>50:
......
else
....
for statment
for x in alist:
print x
for x in range(len(alist))
print x, alist[x] # this put space between items and make formating
break, continue, else statments in loop
function defination
funcation paramter can have defualt values, can have keyword based call
def func1(param1,param2):
...
Complex Number
complex(real,img) functionusing suffix j or J. cn=complex(2,5) or cn = 2+5J
extract complex number cn.real or cn.img
conversion function
float(), int(), long(), round(12.098,2), abs(11.78)
string
can have in double quotes("string"), single quotes('string'), matching triple quotes("""" or '''')
create raw string using r like : hello =r"this is raw string \n\" # it will not treat \n as new line character,
string concate using + operatoer and repeat * operator
hello = "Hello" + "viru"
wrong "This is "+ "wrong"*5
string can accessing using index[2] or slice index[1:10] or negative index [-4], negative index can start counting from right
string methods len(),str(),format
Unicode string use prefix u : hello = u"Helllo¦|¿"
change unicode to other encoding using method encode()
List
list is comma seprated values between square bracket[] : a=["viru",1, 4.5,"this"] # it can contain different types of data.
list can support same kind of index for accessing like strings.
list methods list.append(item), list.extend(L), list.insert(index,item), list.remove(item), list.pop(index), list.sort(), list.count(), list.reverse()
del list[index] : del statement is use for delete entry from list using index or slice index
vec = [2, 4, 6] # list example
sequence
filter(function, sequence) returns a sequence consisting of those items from the sequence for which function(item) is true
map(function, sequence) calls function(item) for each of the sequence’s items and returns a list of the return values.
reduce(function, sequence) returns a single value constructed by calling the binary function function on the first two items of the sequence, then on the result and the next item, and so on.
use sorted() function to sort sequance : sorted(seq)
range() function generate sequance of number(list).
Tuples
A tuple consists of a number of values separated by commas : t = 1,3,67,"hello" empty_tuple=()
Tuples, like strings, are immutable
sequence unpacking : x,y,z=t # t is a tuple
A set is an unordered collection with no duplicate elements.
>>> basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana']
>>> fruit = set(basket) # create a set without duplicates
>>> fruit
set(['orange', 'pear', 'apple', 'banana'])
>>> 'orange' in fruit # fast membership testing
True
dictionary
a dictionary as an unordered set of key: value pairs, with the requirement that the keys are unique (within one dictionary). A pair of braces creates an empty dictionary: {}.
>>> tel = {'jack': 4098, 'sape': 4139}
>>> tel['guido'] = 4127
>>> dict([('sape', 4139), ('guido', 4127), ('jack', 4098)]) # dict() can be use to create dictionary
{'sape': 4139, 'jack': 4098, 'guido': 4127}
looping dictionary use keyword iteritems for k,v in dict1.iteritems():
looping sequance use enumerate keyword for i,v in seq1.enumerate():
looping multiple sequance use zip` for s1,s2 in zip(seq1,seq2):
format functiions
str() humen readable format.
repr() interpreter readable format
rjust(n) righ allinment(justify), ljust(n) left justify, center(), zfill(n) pading with zero
%operatoer can be use for formating like sprintf used in C/C++
File Handling
fh = open(filename, mode) mode values 'w' = write, 'r'= read, 'a'= append 'r+'=read and wirte, defult option is 'r'
data = fh.read(size) return size of data as string, if empty return end of file
line = fh.readline() return a line with new line character '\n' but last doesnot contain '\n'
fh.write(str_data) alway write string data, any other type should convert in string
fh.tell() return file poistion
fh.seek(offset, from) move file position based on from, from have values BOF=0, EOF=2, Cur=1
fh.close() close file resource open
reading
fh = open(filename,'r')
for line in fh
print line
fh.close()
writing
fh = open(filename,'w')
fh.write(content)
fh.close()
pickle moudle
This module used for converting complext object(list, dictionary) to string and vice-versa. pickling, unpickling. for better performance use cPickle module, which is wrriten in C.
pickle.dump(obj, fh) #pickling
obj = pickle.load(fh) #unpickling
Exception Hadnling
Exception handling is working similer to C++/Java.
try:
statements
raise MyException(args, msg) raise work like throw in C++, user define exception
except(RuntimeError, TypeError, NameError): handle multiple exception in single catch
statements
except ValueError: handle single exception
statements
except: handle any kind of exception like (...) in C++
statements
else if no exception occured then this block is exceuted
statements
finally: # this is use to cleanup in every circumstance
statements
Class Concept
Python is a object orianted programming language and it's support OOPS concept similer to C++
class VCalc:
def __init__(self):
print "constructor or initilization "
def add(x,y):
return x+y
def multiply(x,y):
return x*y
Class Derived(Base): # way to inharite class, think in C++ all methods of class are virtual
pass
Runtime information functions
isinstance(obj, int) will be True only if obj.__class__ is int or some class derived from int.
issubclass(bool, int) is True since bool is a subclass of int.
import os http://docs.python.org/library/os.html#module-os
This module help to interface with operating system.
os.getlogin() # get login user name
os.getpid() # get current process id
os.getcwd() # return current working directory
os.chdir("/home/code/testing") # change current working directory
os.system("mkdir /home/viru") # run system command
os.makedirs("/home/viru/report/Trade12222010") # create directory path
os.mkdir(path) # create dirctory
import shutil
This module use to do ile and directory management tasks.
shutil.copyfile('wrong.txt', 'right.txt')
shutil.move('/home/viru/perlCode', '/home/viru/PerlCode')
shutil.copytree(src,dst) #copy recursive tree of directory from source to destination
import sys
This module is use to interact with operating system for program
sys.stderr , sys.stdout, sys.stdin # represent respective stream
sys.exit() # exit from script
sys.call_tracing(fun, args)
sys.path, sys.platform
import re
This module use for regular expression matching, kindly follow this link whenever needed
http://docs.python.org/library/re.html#module-re
re.search(find,string)
re.match()
re.compile()
re.split()
purge(), findall(),sub()
Extra module
math: this is use for maths functions
random: generate random number and random choice
urllib2: access internet urls
smtplib: sending mail
datetime: manipulate date and time
zlib, gzip, bz2,zipfile,tarfile : these are use for data compression
timeit, profile, pstats : performance measurement
unittest, doctest: module for generating testing or validation modules
Important module for creating infrastructure for large applications
xmlrpc, SimpleXMLRPCServer: provide implementation for remote procedure calls(RPC) in xml protocal for wire transfer for data.
email : managing for email message
xml.dom, xml.sax: use for data interchange data formats
csv : use for csv file processing
struct : use for pack and unpack binary data, think like it create the C struct using formats
thread,threading,mutex,Queue, multiprocessing : use for multithreading
logging : logging system
default strip will remove all space.
default strip will remove all space.
def read_file(filename):
fh = open(filename,"r")
for line in fh:
print line.strip("\n")
fh.close();
How to define main function in python
def main():
print "hello word"
if __name__ == "__main__":
main()
How to check file exist or not
def is_file_exist(filename):
ret =0
try:
fh = open(filename)
fh.close()
ret = 1
except IOError, v:
try:
(err_code, err_msg) = v
except:
err_code = 0
err_msg = v
print "I/O Error: " + str(err_msg) + " (" + str(err_code) + ")"
return ret
reading xml file
from xml.dom import minidom
xmldoc = minidom.parse('~/viru/xmlfiles/employee.xml')
print xmldoc.firstChild.toxml()
print xmldoc.childNodes[i]
print xmldoc.getElementsByTagName('Employee')[0].firstChild.data
print xmldoc.getElementsByTagName('Employee')[0].attributes.keys()
print xmldoc.getElementsByTagName('Employee')[0].attributes.values()
print xmldoc.getElementsByTagName('Employee')[0].attributes['department'].value
print xmldoc.getElementsByTagName('Employee')[0].attributes['department'].name
The Python Tutorial http://docs.python.org/tutorial/
Dive Into Python http://diveintopython.org/toc/index.html
======================================================================
======================================================================
