Intro to Python Paul Martin

History Designed by Guido van Rossum Goal: “Combine remarkable power with very clear syntax” Very popular in science labs – "scientists often need to improvise when trying to interpret results, so they are drawn to dynamic languages which allow them to work very quickly and see results almost immediately.“ Guido van Rossum

Compiling and Comments Start Python by typing Python – or Python myFileName # is symbol to comment line – Can be placed on it’s own line or after code

Variable Assignment ‘=‘ is the assignment operator Can apply = operator to many vars at one time – ex. x = y = z = 0

Variable Assignment Cont. No identifier required – height = 5 To declare a floating point variable – width = 3.3 Can declare a variable with an equation – ex. area = width*height #width,height def above

Complex Numbers CmpNum = real + imagj – ex. Cmpnum = j Access real numbers via Cmpnum.real Access imaginary numbers via Cmpnum.imag Magnitude can be found by abs(Cmpnum)

Strings Can be declare with single or double quote – “Hello World” or ‘Hello World’ Can use quote marker inside string when with the escape character ‘\’ – ex. ‘This isn\’t the end’ Can also use the other type of quote marker – ex. “This isn’t the end”

String Concatenation and Length Word = ‘str’ + ‘ing’ Word = ‘str’ ‘ing’ Length = len(Word) – For the above word, length will be equal to 6

String Indexing Start from index 0 Word = ‘HelpA’ – Word[4] = ‘A’ –letter at index 4 – Word[0:2] = ‘He’ –letters index 0 <= x < 2 – Word[0:100] = ‘HelpA’ – Word[:2] = ‘He’ –letters index x < 2 – Word[2:] = ‘lpA’ –letters index x > 2 – Word[3:1] = ‘’ – Accessing in reverse order via the negative sign Word[-2] = ‘p’

Lists List = [‘a’,’b’,2,3] Index Starts from 0 Accessing Elements – List[1] = ‘b’ – List[2:4] = [2, 3] Lists can be nested – List2 = [1,List,2] List length accessed from len(List)

Mutating Lists Lists can be changed – List[3] = List[3] + 40 Elements can be removed/inserted – Insert List[1:1] = [‘aa’,’ab’] – Remove List[0:2] = []

If Statements If x == 0: Do Something elif x == 1: Do Something Else else: Do Anything Else To end statement press enter on an empty line

While and Pass Statements while statement same function as C pass statement does nothing – Used when program requires no action while x == 5: pass #this program will continue as long as x = 5 and #user does not interrupt

Range Statements Useful for performing a loop x amount of times range(10) – creates list [0,1,2,3,4,5,6,7,8,9] range(5,10) – creates list [5,6,7,8,9] range(0,20,5) – Creates list [0,5,10,15]

For Statements Iterates over items of a sequence for x in a: print x break and continue statements same as C – break – exit nearest loop – continue – continue to next iteration of loop

For Else Statements Executed if loop not terminated by break for n in range(2, 10): if n == 11 print ’11 found’ break else: print ‘no 11 found’

Function Definitions def fun(m): if m == 1: print ‘m = 1’ fun(1) – prints ‘m = 1’ fun(2) – prints nothing

References _2010/cs_265_links.htm world/7-programming-languages-the-rise-620