Python Note1 (Startup)

Reference: https://www.tutorialspoint.com/python

• Add path into Windows system.

type path %path%;C:\Python27

• Run a program.

# Method 1
$ python test.py
# Method 2
$ chmod +x test.py     # This is to make file executable
$./test.py

• Module
• Using import to import the modules.

>>> import math
>>> math.floor(32.9)

• Using from [module] import [function] to import a particular function.

>>> from math import sqrt
>>> sqrt(9)

• Multi-Line Statements

total = item_one + \
          item_two + \
          item_three

• Quotation

word = 'word'
sentence = "This is a sentence."
# The triple quotes are used to span the string across multiple lines.
paragraph = """This is a paragraph. It is
made up of multiple lines and sentences."""

• Data Types
• Numbers

# Assign a value to  a variable
var1 = 1
# Delete the reference to a number object
del var1[,var2[...,varN]]

• Strings

str = 'Hello World!'
print str          # Prints complete string
print str[0]       # Prints first character of the string
print str[2:5]     # Prints characters starting from 3rd to 5th
print str[2:]      # Prints string starting from 3rd character
print str * 2      # Prints string two times
print str + "TEST" # Prints concatenated string

• Lists
  A list contains items separated by , and enclosed within [].

list = [ 'abcd', 786 , 2.23, 'john', 70.2 ]
tinylist = [123, 'john']
print list          # Prints complete list
print list[0]       # Prints first element of the list
print list[1:3]     # Prints elements starting from 2nd till 3rd 
print list[2:]      # Prints elements starting from 3rd element
print tinylist * 2  # Prints list two times
print list + tinylist # Prints concatenated lists
list[0] = 1000      # Update the first element of the list

• Tuples
  A tuple consists of a number of values separated by , and enclosed within ().
  Lists' elements and size can be changed, while tuples cannot be updated. Tuples can be thought of as read-only lists.

tuple = ( 'abcd', 786 , 2.23, 'john', 70.2  )
tinytuple = (123, 'john')
print tuple           # Prints complete list
print tuple[0]        # Prints first element of the list
print tuple[1:3]      # Prints elements starting from 2nd till 3rd 
print tuple[2:]       # Prints elements starting from 3rd element
print tinytuple * 2   # Prints list two times
print tuple + tinytuple # Prints concatenated lists

• Dictionary
  Dictionaries are kind of hash table (key-value pairs). A dictionary key can be almost any Python type, but are usually numbers or strings. Values, on the other hand, can be any arbitrary Python object.

dict = {}
dict['one'] = "This is one"
dict[2]     = "This is two"
tinydict = {'name': 'john','code':6734, 'dept': 'sales'}
print dict['one']       # Prints value for 'one' key
print dict[2]           # Prints value for 2 key
print tinydict          # Prints complete dictionary
print tinydict.keys()   # Prints all the keys
print tinydict.values() # Prints all the values

Data Types	Brackets
List	[]
Tuple	()
Dictionary	{}

• Loops
• for Loop

for iterating_var in sequence:
   statements(s)

Executes a sequence of statements multiple times and abbreviates the code that manages the loop variable.

fruits = ['banana', 'apple',  'mango']
# 1st method
for fruit in fruits:      
   print 'Current fruit :', fruit
# 2nd method
for index in range(len(fruits)):
   print 'Current fruit :', fruits[index]
# 3rd method
for index in range(len(fruits)):
   print 'Current fruit :', fruits[index]
else:
  print 'end'

• while Loop

while expression:
   statement(s)

Repeats a statement or group of statements while a given condition is TRUE.

var = 1
while var == 1 :  # This constructs an infinite loop
   num = raw_input("Enter a number  :")
   print "You entered: ", num

Using else Statement with Loops:

• If the else statement is used with a for loop, the else statement is executed when the loop has exhausted iterating the list.

• If the else statement is used with a while loop, the else statement is executed when the condition becomes false.

• nested Loop
  You can use one or more loop inside any another while, for or do..while loop.