Introduction to Python and Matplotlib

Introduction to Python and Matplotlib

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  Introduction to Python andScientific Python Fran¸cois Bianco Unige 21th Dec 2011 Fran¸cois Bianco Introduction to Python
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  Outlook 1 Python featuresand syntax 2 Examples, pylab, and iPython 3 Flat files examples Based on : Learn Python in 10 minutes : http://www.poromenos.org/tutorials/python Python documentation : http://docs.python.org/index.html Matplotlib : http://matplotlib.sourceforge.net/ Scipy : http://www.scipy.org/ Fran¸cois Bianco Introduction to Python
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  Python is Strongly typed(i.e. types are enforced) Dynamically, implicitly typed (i.e. you don’t have to declare variables) Python is case sensitive (i.e. var and VAR are two different variables) object-oriented (i.e. everything is an object) able to handle memory by itself (i.e has a garbadge collector) Fran¸cois Bianco Introduction to Python
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  Example Example l i st = [1 ,1.1 ,1+1 j , ’ 1 ’ , True ] for element in l i s t : print element , type ( element ) , element==1.1 No mandatory statement termination character Blocks are specified by indentation (4 spaces, or 1 tab) Statements that expect an indentation level end in a colon “:” Values are assigned (in fact, objects are bound to names) with the equals sign “=” Equality testing is done using two equals signs “==” Fran¸cois Bianco Introduction to Python
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  Data structures Three maindata structures list = [1,2,3,4,5,6] are mutable tuples = (1,2,3,4,5,6) are unmutable dictionary = { ’key’:’value’, ’answer’:42, ’obj’:list } also called hash tables, access by key List and tuples are access by index : list[index] (see array slicing). Dictionary by key dictionary[’answer’]. Fran¸cois Bianco Introduction to Python
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  Modules loading Classes andfunctions are stored in modules from math import s i n #only one f u n c t i o n s i n ( 0 . 3 ) import math #the whole module keeping namespace math . s i n ( 0 . 3 ) from math import * #the whole module cos ( 0 . 3 ) import m a t p l o t l i b as mptl #rename namespace mptl . c o n v e r t e r () Fran¸cois Bianco Introduction to Python
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  Other features ofPython Modern way of handling errors try : f i l e O b j = open ( ’ fileName . t x t ’ ) except IOError : print ErrorMessage Lambda functions f i t f u n c = lambda x , y : s q r t ( x/y ) f i t f u n c ( 4 . 5 , 2 . 3 ) Fran¸cois Bianco Introduction to Python
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  Other features ofPython Classes, functions... def functionName ( param , optionalParam=value ) : . . . class C h i l d C l a s s ( ParentClass ) : . . . Automatic documentation generation (with Doxygen) def toggleImages ( s e l f , event ) : ””” Toggle the two images according to the t r i g g e r event . param event Key or mouse event t r i g g e r i n g the f u n c t i o n ””” Fran¸cois Bianco Introduction to Python
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  Flow control statements Example:Fibonnaci in a simple while loop a , b = 0 ,1 while b<10: print b a , b = b , a+b Easy variables assignation, and permutation, no extra variable needed. Fran¸cois Bianco Introduction to Python
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  Array slicing Example: accessto specific elements in an array x = arange (10) #c r e a t e a vector from 0 to 9 x #the whole vector x [ 0 ] #only the f i r s t element x [ 3 ] #the 3 rd element x [ −2] #the second l a t e s t element x [ 1 : 4 ] #elements from 1 to 4 x [ : 5 ] #elements up to 5 x [ −3:] #the three l a s t elements Fran¸cois Bianco Introduction to Python
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  Array masking Example: createa mask on an array a = arange (10) mask = (( a % 2) == 0) a [ mask ] = 0 This sets all the even value in a to 0. Fran¸cois Bianco Introduction to Python
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  Easy plot Example :plot with label and LATEX title p l o t ( arange (5)) x l a b e l ( ’ Index ’ ) y l a b e l ( ’Sum ’ ) t i t l e ( r ’ $sum { i =0}ˆ i n f t y i $ ’ ) Fran¸cois Bianco Introduction to Python
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  Display matrix asan image Example : create an image from a matrix x = randn (20 ,20) #c r e a t e a random 20 x20 matrix imshow ( x ) #p i x e l s c a l e imshow ( x , extent =(0 ,1 ,0 ,1)) #add custom s c a l e Fran¸cois Bianco Introduction to Python
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  Histogramm plot Example :create an histogramm plot mu, sigma = 100 , 15 x = mu + sigma * randn (10000) h i s t ( x ,100) Fran¸cois Bianco Introduction to Python
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  Many plots Example :create two plots with legend t = arange (0 ,5 ,0.05) # Vect . 0 , 0 . 0 5 , 0 . 1 , . . . , 5 s1=s i n (2* pi * t ) s2=s1 *exp(−t ) p l o t ( t , s1 , ’g−−o ’ , t , s2 , ’ r : s ’ ) # custom s t y l e s legend (( ’ Sin wave ’ , ’Damped exp . ’ )) Fran¸cois Bianco Introduction to Python
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  iPython Usefull magic commandsin iPython help ( obj ) #Show help obj ? #Show doc s t r i n g obj ?? #Show source code #r e t u r n l a s t value %who #l i s t o b j e c t s %whos #d e t a i l l e d o b j e c t s l i s t %h i s t −n #h i s t o r y without l i n e number %exec In [ 4 : 7 ] #redo l i n e 4 to 7 %e d i t 4:7 #e d i t l i n e 4 to 7 in s c r i p t %run #launch a s c r i p t % p f i l e #show source f i l e content You want more of it ? Try %lsmagic Fran¸cois Bianco Introduction to Python
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  Pro and cons Cons NoGUI Documentation spread on different websites Requires basics programming skills Pro Easy to learn Work on every plateform (WinXP,Vista,MacOS,Linux,...) Could be bind to Gwyddion It’s a free software Fran¸cois Bianco Introduction to Python
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  Other good reasonsto learn Python Used by different universities and research centers : University of Montreal, Princeton University, Space Telescope Science Institute, Los Alamos National Laboratory, UC Berkeley, CERN, NASA ... If you want to look for a job in some “small” companies : Google, HP, IBM, Nokia, Thawte Consulting (SSL certificates), EA Games, Industrial Light & Magic (Hollywood), ... Fran¸cois Bianco Introduction to Python
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  The end “There shouldbe one – and preferably only one – obvious way to do it.” Tim Peters, The Zen of Python Fran¸cois Bianco Introduction to Python