Python Basics
Python does not use brackets to structure code, instead it uses whitespaces.
To define a variable
you do not have to specify the datatype.
find the datatype:
print type(x)
comment
# This is a single line comment
''' This is a multi-line Python
comment. '''
ask the user for input
using the raw_input function:
#!/usr/bin/env python
x = int(raw_input("Enter x:"))
y = int(raw_input("Enter y:"))
sum = x + y
print sum
In the latest Python version you can use the input() function instead:
x = int(input("Enter x:"))
do operations on strings:
s = "Hello Python"
print s # prints whole string
print s[0] # prints "H"
print s[0:2] # prints "He"
print s[2:4] # prints "ll"
print s[6:] # prints "Python"
print s + ' ' + s # print concatenated string.
print s.replace('Hello','Thanks') # print a string with a replaced word
Python String compare
sentence = "The cat is brown"
q = "cat"
if q == sentence:
print 'equal'
else:
print 'not equal'
Python String contains
sentence = "The cat is brown"
q = "cat"
if q in sentence:
print q + " found in " + sentence
list
l = [ "Drake", "Derp", "Derek", "Dominique" ]
print l # prints all elements
print l[0] # print first element
print l[1] # prints second element
l.append("Victoria") # add element.
print l # print all elements
l.remove("Derp") # remove element.
l.remove("Drake") # remove element.
print l # print all elements.
l.sort() # sorts the list in alphabetical order
l.reverse() # reverse order.
iteration:
items = [ "Abby","Brenda","Cindy","Diddy" ]
for item in items:
print item
A tuple is a sequence of data.
It is defined as a sequence of elements separated by a comma.
point = (3,4)
point2 = (2,6,12)
print point
print point[0]
print point[1]
print point2
print point2[0]
print point2[1]
A dictionary
is an unordered set of key:
words = {}
words["Hello"] = "Bonjour"
words["Yes"] = "Oui"
words["No"] = "Non"
words["Bye"] = "Au Revoir"
print words # print key-pairs.
del words["Yes"] # delete a key-pair.
print words # print key-pairs.
words["Yes"] = "Oui!" # add new key-pair.
print words # print key-pairs.
Output:
{'Yes': 'Oui', 'Bye': 'Au Revoir', 'Hello': 'Bonjour', 'No': 'Non'}
{'Bye': 'Au Revoir', 'Hello': 'Bonjour', 'No': 'Non'}
{'Yes': 'Oui!', 'Bye': 'Au Revoir', 'Hello': 'Bonjour', 'No': 'Non'}
Datatype casting
| Function | Description |
|---|---|
| int(x) | Converts x to an integer |
| long(x) | Converts x to a long integer |
| float(x) | Converts x to a floating point number |
| str(x) | Converts x to an string. x can be of the type float. integer or long. |
| hex(x) | Converts x integer to a hexadecimal string |
| chr(x) | Converts x integer to a character |
| ord(x) | Converts character x to an integer |
x = 3
y = 2.15315315313532
print "We have defined two numbers,"
print "x = " + str(x)
print "y = " + str(y)
a = "135.31421"
b = "133.1112223"
c = float(a) + float(b)
print c
if
print "Guess my age"
guess = int(raw_input("Guess: "))
if guess > 10 and guess < 20:
print "In range"
else:
print "Out of range"
function
def doA():
a = 5
def doB(a):
print a # this will work
doB(3)
For loop 1
items = [ "Abby","Brenda","Cindy","Diddy" ]
for item in items:
print item
For loop 2
for x in range(1,10):
for y in range(1,10):
print "(" + str(x) + "," + str(y) + ")"
while loop
while button_not_pressed:
drive()
Python OOP
class in Python
class User:
name = ""
def __init__(self, name):
self.name = name
def sayHello(self):
print "Hello, my name is " + self.name
# create virtual objects
james = User("James")
david = User("David")
eric = User("Eric")
# call methods owned by virtual objects
james.sayHello()
david.sayHello()
inheritance
class User:
name = ""
def __init__(self, name):
self.name = name
def printName(self):
print "Name = " + self.name
class Programmer(User):
def __init__(self, name):
self.name = name
def doPython(self):
print "Programming Python"
brian = User("brian")
brian.printName()
diana = Programmer("Diana")
diana.printName()
diana.doPython()
polymorphism
class Bear(object):
def sound(self):
print "Groarrr"
class Dog(object):
def sound(self):
print "Woof woof!"
def makeSound(animalType):
animalType.sound()
bearObj = Bear()
dogObj = Dog()
makeSound(bearObj)
makeSound(dogObj)
polymorphism with abstract class
class Document:
def __init__(self, name):
self.name = name
def show(self):
raise NotImplementedError("Subclass must implement abstract method")
class Pdf(Document):
def show(self):
return 'Show pdf contents!'
class Word(Document):
def show(self):
return 'Show word contents!'
documents = [Pdf('Document1'),
Pdf('Document2'),
Word('Document3')]
for document in documents:
print document.name + ': ' + document.show()
Output:
Document1: Show pdf contents!
Document2: Show pdf contents!
Document3: Show word contents!
another example
of abstract class:
class Car:
def __init__(self, name):
self.name = name
def drive(self):
raise NotImplementedError("Subclass must implement abstract method")
def stop(self):
raise NotImplementedError("Subclass must implement abstract method")
class Sportscar(Car):
def drive(self):
return 'Sportscar driving!'
def stop(self):
return 'Sportscar breaking!'
class Truck(Car):
def drive(self):
return 'Truck driving slowly because heavily loaded.'
def stop(self):
return 'Truck breaking!'
cars = [Truck('Bananatruck'),
Truck('Orangetruck'),
Sportscar('Z3')]
for car in cars:
print car.name + ': ' + car.drive()
Output:
Bananatruck: Truck driving slowly because heavily loaded.
Orangetruck: Truck driving slowly because heavily loaded.
Z3: Sportscar driving!
Reference: Python Beginner by pythonspot.com
Python tricks
start a simple HTTP server:
python -m SimpleHTTPServer
Using Zip
to combine arrays
>>> b = [[1, 2, 3, 4], [6, 5, 4, 3]]
>>> zip(*b)
[(1, 6), (2, 5), (3, 4), (4, 3)]
We know that “array.reverse()” will reverse an array.
How do we reverse a string?
>>> s = "Hello world"
>>> s = s[::-1]
>>> print s
dlrow olleH
Swapping variables
>>> a = 1
>>> b = 3
>>> b,a = a,b
>>> print a
3
>>> print b
1
Reference: Fun tricks with Python, pythonspot.com