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Introduction of Python

Introduction of Python . Based on: Learning Python By Mark Lutz & David Ascher , O'Reilly Introduction to Python By Guido van Rossum Learning Python By Mark Lutz & David Ascher , O'Reilly 10 Reasons Python Rocks for Research By Hoyt Koepke. A Brief History.

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Introduction of Python

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  1. Introduction of Python Based on: Learning Python By Mark Lutz & David Ascher, O'Reilly Introduction to Python By Guido van Rossum Learning Python By Mark Lutz & David Ascher, O'Reilly 10 Reasons Python Rocks for Research By Hoyt Koepke

  2. A Brief History • Invented in 1990 by Guido Van Rossum • The name ‘Python’ stems from • "Monty Python's Flying Circus“ • Intended to be a scripting language on Amoeba OS • Python was influenced by ABC and Modula-3 • First public release was in 1991

  3. Python • On the Web: www.python.org

  4. Python Advantages • Object-Oriented • Dynamic Type Checking makes it inherently generic – C++ templates for free! • Free, as in Open Source free • Portable • Powerful language constructs / features • Powerful toolkit / library • Mixable with other languages • Easy to use & learn

  5. Features for writing codes • Great for learning the language • Great for experimenting with the library • Great for testing your own modules • High efficiency • Clarity

  6. Python Principles • Python treats everything as an object • Python is an interpreter • It gives immediate results • It generates byte code (similar to Java)

  7. Running Python • Interactively from console: • C:>python • >>>print2*3 • 6 • As Python module files: • C:>python mypgm.py Interactive prompt No statement delimiter Python modules are text files with .py extensions

  8. Simple examples • Built-in and explicit print • >>>"Hello all" • 'Hello all' • >>>print"A b" • A b • >>>ALongName = 177 / 3 • >>>ALongName • 59 Builtin print gives double quotes as single quotes. " and ' quotes are same. print statement removes quotes

  9. Built-in Object Types

  10. Basic Operations • Assignment creates names • s = 'A string'# s is created • Names can be any length • Names are case sensitive • >>> A = 1; a = 2; A+a • 3 Semicolons separates statements on the same line

  11. String Formatting Adjacent strings are concatenated, like in C • Like C's printf with similar specifiers • "It's " '%d great life!' % 1 • "It's 1 great life!" • '%s %s much' % ("Python's", 2) • "Python's 2 much" • C's backslash conventions used • Raw strings take backslashes literally • print "a\tc" # outputs a c • print R"a\tc" # outputs a\tc

  12. String Operations Range includes lower bound and excludes upper bound Suppress new line on output

  13. Lists • Sequence of mutable heterogeneous objects (items can be changed in-place).

  14. Dictionaries • Mapping of unordered immutable keys to mutable heterogeneous objects.

  15. IF Statement • General form example: • if 'a' <= c <= 'z': • print 'Lower case letter' • elif 'A' <= c <= 'Z': # optional • print 'Upper case letter' • else:# optional • print 'Not a letter'

  16. WHILE Statement • General format: while <test> : # loop conditional <stmt-block1> # loop body else: # optional - run <stmt-block2> # if no break used a = 0; b = 5 while a < b : print a, # outputs 0 1 2 3 4 a = a + 1

  17. BREAK, CONTINUE, PASS • break terminates the innermost executing loop and transfer control after the loop. • continue immediately transfers control to the top of the innermost executing loop. • pass is the no-op statement in Python. • while <test0> :# loop header • <stmts1> # run if test0 true • if <test1> :break# exit, skip else • if <test2> :continue# go to loop header • <stmts2> # not run if test2 true • else: • <stmts3> # run if didn't hit break

  18. FOR Statement • General format: for <target> in <object> : # loop header <stmt-block1> # loop body else: # optional, run else clause <stmt-block2> # if no break used sum = 0 for x in [1, 2, 3, 5] : sum = sum + x sum # outputs 11

  19. Modules • Modules are implemented using files. • Module source files have a .py extension. • Compiled byte code modules have .pyc extension.

  20. Loading Modules • There are 3 ways to load a module:

  21. Import Statement • Using the import statement: # sigma1.py - test module counter = 1 def Sigma(L) : sum = 0 for x in L : sum = sum + x return sum print "Loaded module sigma1" >>> import sigma1 Loaded module sigma1 >>> sigma1.counter 1 >>> sigma1.Sigma([1, 2, 3]) 6 >>> sigma1.counter = 2 >>> import sigma1 >>> sigma1.counter 2

  22. Reasons Python Rocks for Research • Holistic Language Design • Readability • Balance of High Level and Low Level Programming • Language Interoperability • Documentation System • Hierarchical Module System • Data Structures • Portable • Available Libraries • Free

  23. Python VS Matlab • Python is totally free. Matlab is not. • Python is a general-purpose language. Matlab is purely for scientific computing, although it does a great job at it. • Python syntax is beautiful. • Python is inherently object oriented. • Python is fast enough. • Python has great community among programmers, scientists, mathematicians, and engineers, great libraries. • Python packages can do nearly everything Matlab can do for signal processing.

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