Python
Quick Reference I


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index


print


print 'hello'
print "hello hello"
print """hello hello hello"""
print """hello -
    hello hello"""
pi = 3.14159
print 'pi is %f' % pi
print '2pi is %f' % (pi * 2)
print 'pi is %f 2pi is %f' % (pi,pi*2)   
print 'pi is %1.3f' % pi

single quotations
double quotations
triple quotations
triple quotations can span multiple lines of text
variable assignment
print a single variable
print + arithmetic
print multiple values
formatting ie. "pi is 3.142"



setting variables


pi = 3.14159
age = 21
numAsStr = '32'
num = int(numAsStr)

pi is assigned as a float
age is assigned as an integer
numAsStr is assigned as a string
the int() function converts a numeric string to an integer



if-elif-else


padding = ""
val = 43
if val < 10:
    padding = '000%d' % val
elif val < 100:
    padding = '00%d' % val
else:
    padding = '0%d' % val
if not padding == "":
    print padding

the code shown on the left creates a numeric string with 4 padding digits, for example, 43 becomes "0043"





example of a "not-equal-to" test



for loops


from sys import stdout as out
columns = 3
rows = 4
for i in range(columns):
    for j in range(rows):
        out.write('%d%d '%(i+1, j+1))   
        if j == 3:
            print ''

pets = ['cat','dog','fish']
for pet in pets:
    print pet



the output of the nested "for" loops is,
    11 12 13 14
    21 22 23 24
    31 32 33 34
note the use of the write() function
insert a newline

printing each item in the list



Using Strings


english = 'Hello'
italian = "Ciao"
siswati = """sawubona"""
go = 'hamba'
well = 'kahle'
farewell = go + ' ' + well
farewell = 'hamba' ' ' 'kahle'
print('num chars is %d') % len(farewell)    
siswati = 'Khisimusi Lomuhle'
merry = siswati[10:]
christmas = siswati[:9]
christmas[10] = 'l'
christmas = 'Khisimusi lomuhle'

single quotations
double quotations
triple quotations
assign two string variables

concatenating string variables
concatenating string literals
querying the length of a string

slicing - from the 10th char
slicing - upto the 9th char
error - cannot change individual chars
but the entire string can be re-assigned

Other String Methods [docs]

 

txt = "Pixar's Renderman"
txt.find('man')
txt.replace('man', 'Man')
txt.capitalize()
txt.upper()
txt.lower()
txt.isalpha()

txt.split() # returns "Pixar's" and "RenderMan"
txt * 4 # repeat four times
txt.lstrip("Pixar's ") # remove "Pixar's "
txt.rstrip(' Renderman') # remove "Renderman "
txt.endsWith('n')
txt.startswith('P')
txt.isdigit()



Using Lists


places = []
places.append('germany')
places.append('swaziland')
places.append('france')
places.extend(['italy','usa','brazil'])    
print places[0]
print '%d places' % (len(places))
places.sort()
print places[len(places)-2:]
europe = places[1:4]
print europe

create an empty list
add items one at a time


add several items
print the first item
print the size of the list
sort the list alphabetically
print the last two items
copy a sliced portion of a list

Other List Methods [docs]

 

lst = ["Pixar's", 'RenderMan']
lst.insert(0, 'Using')
lst.remove('RenderMan') # deletes "RenderMan"
lst.pop(0) # deletes and returns 'Using'

lst.index("Pixar's")
lst.reverse()



Using Dictionaries


lut = {'color space': 'rgb', 
        'orange': [1.0, 0.4, 0.2],
        'purple': [0.6, 0.0, 0.6]}
items = [('color space', 'rgb'), 
         ('orange', [1.0, 0.4, 0.2]), 
         ('purple', [0.6, 0.0, 0.6])]
lut = dict(items)
print lut['color space']
print lut['orange']
  
if not lut.has_key('blue'):
    print 'no blue'
if 'blue' not in lut:
    print 'no blue'
print lut.keys()
print lut.values()
  
  
  
print len(lut)
r,g,b = lut['orange']
print '%1.3f,%1.3f,%1.3f' % (r,g,b)  
lut['purple'] = [1.0,0.2,0.8]

define a simple color lookup table


rgb
[1.0, 0.40000000000000002, 0.20000000000000001]

no blue

no blue
['orange', 'purple', 'color space']
[[1.0, 0.40000000000000002, 0.20000000000000001], [0.59999999999999998, 0.0, 0.59999999999999998], 'rgb']
3
get the rgb components
1.000, 0.400, 0.200
assign new values to "purple"

Other Dictionary Methods [docs]

 






© 2002- Malcolm Kesson. All rights reserved.