Knowledge flow - Python Programming

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This eBook contents is for informational and study purposes only.

• graphical user interfaces
• web frameworks
• multimedia
• databases
• networking
• communications
• test frameworks
• automation
• web scraping
• documentation tools
• system administration
• scientific computing
• text processing
• image processing

Development environment

• Python implements function like a command line interpreter the user enters the statement in a sequenced manner and receives the results instantly.
• Python shell implement features like auto-completion, retention of session state and syntax highlighting.

Implementation

• Google started a project in 2009 termed Unladen Swallow whose aim was increasing the speed of Python interpreter as well as improving its multithreading ability to scale to thousands of cores.
  • graphical user interfaces
  • web frameworks
  • multimedia
  • databases
  • networking
  • communications
  • test frameworks
  • automation
  • web scraping
  • documentation tools
  • system administration
  • scientific computing
  • text processing
  • image processing
  Development environment
  • Python implements function like a command line interpreter the user enters the statement in a sequenced manner and receives the results instantly.
  • Python shell implement features like auto-completion, retention of session state and syntax highlighting.
  Implementation
  • Google started a project in 2009 termed Unladen Swallow whose aim was increasing the speed of Python interpreter as well as improving its multithreading ability to scale to thousands of cores.

    Later the project lost Google's back up as well as its main developers.

  • Integrated CPython transforms byte code to machine code at runtime and also produces codes specialized for certain data types that is faster than the standard Python code.
  
  Pythons Basic Syntax
  Python sample program $ Python Python 2.4.3 (#1, Nov 11 2010, 13:34:43) [GCC 4.1.2 20080704 (Red Hat 4.1.2-48)] on linux2 Type"help","copyright","credits" or"license" for more information Following should be written on the command prompt and the enter key should be pressed >>> print "Hello, Python!"; Output Hello, Python! Identifiers Here are following identifiers conventions declared for python.
  • All the identifiers are in lower case except the class name which would start with an upper case.
  • Identifiers are used for privacy, starting with a single leading underscore.
  • If two leading underscore are contained then it contains a strong privacy.
  • If it ends with two different underscores then the language is defined special name.
  Lines and Indentation Various spaces in indentation are variables, and almost whole statement must be inside the block must be indented the similar amount. Example if True: print "True" else: print "False" Second block that would produce an error is as follows. if True: print "Answer" print "True" else: print "Answer" print "False" Following is an example for blocks with various statements. #!/usr/bin/python import sys try: # open file stream file = open(file_name, "w") except IOError: print "There was an error writing to", file_name sys.exit() print "Enter '", file_finish, print "' When finished" while file_text != file_finish: file_text = raw_input("Enter text: ") if file_text == file_finish: # close the file file.close break file.write(file_text) file.write("\n") file.close file_name = raw_input("Enter filename: ") if len(file_name) == 0: print "Next time please enter something" sys.exit() try: file = open(file_name, "r") except IOError: print "There was an error reading file" sys.exit() file_text = file.read() file.close() print file_text Command line argument Basic informations are provided through this so that one can know how to run these programs. [-c cmd | -m mod | file | -] [arg] ... [-c cmd | -m mod | file | -] [arg] ...

  Options and arguments (and corresponding environment variables): -c cmd : program passed in as string (terminates option list) -d : debug output from parser (also PYTHONDEBUG=x) -E : ignore environment variables (such as PYTHONPATH) -h : print this help message and exit. Accessing command line argument It provides a getopt module for accessing a command line. Syntax $ python test.py arg1 arg2 arg3 There are two purpose of it which is as follow.

  • List of command line arguments are provided through sys.argv.
  • And the total number of command line is Len (sys.argv).
  Example #!/usr/bin/python import sys print 'Number of arguments:', len(sys.argv), 'arguments.' print 'Argument List:', str(sys.argv) Next step is to run above script as follows. $ python test.py arg1 arg2 arg3 Output Number of arguments: 4 arguments.
  • Numbers
  • String
  • List
  • Tuple
  • Dictionary
  Numbers It contains numeric values and is created when value is assigned to them.
  • Numbers
  • String
  • List
  • Tuple
  • Dictionary
  Numbers It contains numeric values and is created when value is assigned to them.

  Example var1 = 1 var2 = 10 Syntax of delete statement is as follows. del var1[,var2[,var3[....,varN]]]] Syntax for deleting multiple or single objects are as follows. del var del var_a, var_b It supports four different numerical styles which are as follows.

  • Int
  • Long
  • Float
  • Complex
  Strings
  • It is identified as the set of characters.
  • The plus sign is represented as the string concatenation operator.
  • Similarly the asterisk is represented as the repetition operator.
  Example #!/usr/bin/python str = 'Hello World!' print str # Prints complete string print str[0] # Prints first character of the string print str[2:5] # Prints characters starting from 3rd to 5th print str[2:] # Prints string starting from 3rd character print str * 2 # Prints string two times print str + "TEST" # Prints concatenated string. Output Hello World! H llo llo World! Hello World!Hello World! Hello World!TEST. List These are written in between the brackets and with commas.

  Example #!/usr/bin/python list = [ 'abcd', 786 , 2.23, 'john', 70.2 ] tinylist = [123, 'john'] print list # Prints complete list print list[0] # Prints first element of the list print list[1:3] # Prints elements starting from 2nd till 3rd print list[2:] # Prints elements starting from 3rd element print tinylist * 2 # Prints list two times print list + tinylist # Prints concatenated lists Output ['abcd', 786, 2.23, 'john', 70.200000000000003] abcd [786, 2.23] [2.23, 'john', 70.200000000000003] [123, 'john', 123, 'john'] ['abcd', 786, 2.23, 'john', 70.200000000000003, 123, 'john'] Tuples It is also a similar sequenced data type like list. Example #!/usr/bin/python tuple = ( 'abcd', 786 , 2.23, 'john', 70.2 ) tinytuple = (123, 'john') print tuple # Prints complete list print tuple[0] # Prints first element of the list print tuple[1:3] # Prints elements starting from 2nd till 3rd print tuple[2:] # Prints elements starting from 3rd element print tinytuple * 2 # Prints list two times print tuple + tinytuple # Prints concatenated lists Output ('abcd', 786, 2.23, 'john', 70.200000000000003) Abcd (786, 2.23) (2.23, 'john', 70.200000000000003) (123, 'john', 123, 'john') ('abcd', 786, 2.23, 'john', 70.200000000000003, 123, 'john' Dictionary It is a kind of hash table and the values are enclosed in the curly bracket. Example #!/usr/bin/python dict = {} dict['one'] = "This is one" dict[2] = "This is two" tinydict = {'name': 'john','code':6734, 'dept': 'sales'} print dict['one'] # Prints value for 'one' key print dict[2] # Prints value for 2 key print tinydict # Prints complete dictionary print tinydict.keys() # Prints all the keys print tinydict.values() # Prints all the values Output This is one This is two {'dept': 'sales', 'code': 6734, 'name': 'john'} ['dept', 'code', 'name'] ['sales', 6734, 'john']

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