Commands to run


basics-

Interactive mode-

print("hello python")

Script mode-

hello.py
print ("hello python!!")
chmod +x hello.py
./hello.py

Comments in python-
open the same hello.py
add comments in it.

Variables in python-
p
basics_python.py
count   = 10           # An integer assignment
miles   = 1000.0       # A floating point
name    = "Devendra"       # A string

print (count)
print (miles)
print (name)

a, b, c = 1, 2, "Devendra"
print (a)
print (b)
print (c)


I/O variable-
a=input("Enter value for a:")
print(a)


String Manipulation-

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])
print (str * 2)      # Prints string two times
print (str + "TEST") # Prints concatenated string

Lists -

list = [ 'abcd', 86 , 1.3, 'devendra', 9.6 ]
tinylist = [123, 'devendra']

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 (list[::2])
print (tinylist * 2)  # Prints list two times
print (list + tinylist) # Prints concatenated lists
explain append function.

exercise-

Write a program that takes a list of numbers (for example, a = [5, 10, 15, 20, 25]) and makes a new list of only 
the first and last elements of the given list. For practice, write this code inside a function.

list=[5, 10, 15, 20, 25]
list_ends(list):
    return [list[0], list[len(list)-1]]


Dictionary-

dict = {}
dict['one'] = "This is one"
dict[2]     = "This is two"

tinydict = {'name': 'Devendra','code':64, 'dept': 'marketing'}


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

Exercise-
Write a Python program to add key to a dictionary.

Sample Dictionary : {0: 10, 1: 20}
Expected Result : {0: 10, 1: 20, 2: 30}
d = {0:10, 1:20}  
print(d)  
d.update({2:30})  
print(d)


If else loop-

var = 100

if ( var  == 100 ) :
print ("Value of expression is 100")
else
print ("The value of expression is not 100")


var = 100

if var < 200:
   print ("Expression value is less than 200")
   if var == 150:
      print ("Which is 150")
   elif var == 100:
      print ("Which is 100")
   elif var == 50:
      print ("Which is 50")
elif var < 50:
   print ("Expression value is less than 50")
else:
   print ("Could not find true expression")

for loop-

for letter in 'Python':     # First Example
   print 'Current Letter :', letter

fruits = ['banana', 'apple',  'mango']
for fruit in fruits:        # Second Example
   print 'Current fruit :', fruit

for num in range(10,20):  #to iterate between 10 to 20
   for i in range(2,num): #to iterate on the factors of the number
      if num%i == 0:      #to determine the first factor
         j=num/i          #to calculate the second factor
         print '%d equals %d * %d' % (num,i,j)
         break #to move to the next number, the #first FOR
   else:                  # else part of the loop
      print num, 'is a prime number'

while loop-

count = 0
while (count < 9):
   print 'The count is:', count
   count = count + 1

count = 0
while count < 5:
   print count, " is  less than 5"
   count = count + 1
else:
   print count, " is not less than 5"


Functions-


def quadcube(x):
return x**2, x**3

a=quadcube(5)
print(a)





File I/O

f=open("hello.py",r)
data=f.read()
print (data)

f=open("hello.py",w)
f.write( "Python is a great language.\nYeah its great!!\n")
data=f.read()
print (data)

Command-Line Arguments:

import sys
print('version is', sys.version)

python sys-version.py



import sys

def main():
filename = sys.argv[0]
f=open(filename,r)
data=f.read()
print (data)

main()


Handling Standard Input:


import sys

count = 0
for line in sys.stdin:
    count += 1

print(count, 'lines in standard input')




Errors:

Syntax Error:

def some_function()
    msg = "hello, world!"
    print(msg)
     return msg

Variable Name Error:

for number in range(10):
    count = count + number
print("The count is: " + str(count))



# Program to convert kilometers into miles 
# Input is provided by the user in kilometers

# take input from the user
kilometers = float(input('How many kilometers?: '))

# conversion factor
conv_fac = 0.621371

# calculate miles
miles = kilometers * conv_fac
print('%0.3f kilometers is equal to %0.3f miles' %(kilometers,miles))

# Python Program to find the area of triangle
# Three sides of the triangle a, b and c are provided by the user

a = float(input('Enter first side: '))
b = float(input('Enter second side: '))
c = float(input('Enter third side: '))

# calculate the semi-perimeter
s = (a + b + c) / 2

# calculate the area
area = (s*(s-a)*(s-b)*(s-c)) ** 0.5
print('The area of the triangle is %0.2f' %area)

Defensive Programming
numbers = [1.5, 2.3, 0.7, -0.001, 4.4]
total = 0.0
for n in numbers:
    assert n > 0.0, 'Data should only contain positive values'
    total += n
print('total is:', total)

Exercise
Explain in words what the assertions in this function check, and for each one, give an example of input that will make that assertion fail.
def running(values):
    assert len(values) > 0
    result = [values[0]]
    for v in values[1:]:
        assert result[-1] >= 0
        result.append(result[-1] + v)
        assert result[-1] >= result[0]
    return result