README.md

Basics of Python programming

Interpreter

1. Open a terminal by pressing [CTRL]+[ALT]+[T] keys

2. Type python3 and press [ENTER]

   

3. Try out below mentioned examples, and understand what's happening.

4. To exit the interpreter, type quit() and press [ENTER]

Numerical Operators

• +, -, *, /, // (floor division), % (remainder), ** (power), =

Strings

1. Run following two commands and explain the difference in output

   >>> print('C:\some\name')
   >>> print(r'C:\some\name')

   Which of the above represents a raw string?

2. String literals can span multiple lines by using triple-quotes: """...""" or '''...'''.

3. Strings can be concatenated with the + operator, and repeated with *

   >>> 3 * 'un' + 'ium'

4. Slicing

   >>> word = 'Python'
   >>> word[0:2]  # characters from position 0 (included) to 2 (excluded)
   >>> word[2:5]  # characters from position 2 (included) to 5 (excluded)
   >>> word[:2]   # character from the beginning to position 2 (excluded)
   >>> word[4:]   # characters from position 4 (included) to the end
   >>> word[-2:]  # characters from the second-last (included) to the end

   Note how the start is always included, and the end always excluded. This makes sure that s[:i] + s[i:] is always equal to s:

   

Lists

>>> cubes = [1, 8, 27, 65, 125]
>>> cubes.append(216)  # add the cube of 6

>>> letters = ['a', 'b', 'c', 'd', 'e', 'f', 'g']
>>> letters[2:5] = ['C', 'D', 'E']
>>> letters[2:5] = []
>>> letters[:] = []
>>> len(letters)

Control Flow Tools

if

>>> x = int(input("Please enter an integer: "))
Please enter an integer: 42
>>> if x < 0:
...     x = 0
...     print('Negative changed to zero')
... elif x == 0:
...     print('Zero')
... elif x == 1:
...     print('Single')
... else:
...     print('More')
...

for

>>> # Measure some strings:
... words = ['cat', 'window', 'defenestrate']
>>> for w in words:
...     print(w, len(w))
...

while

>>> # Fibonacci series:
... a, b = 0, 1
>>> while a < 1000:
...     print(a, end=',')
...     a, b = b, a+b
...
0,1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,

range()

>>> for i in range(5):
...     print(i)
...

>>> list(range(0, 10, 3))
[0, 3, 6, 9]

>>> a = ['Mary', 'had', 'a', 'little', 'lamb']
>>> for i in range(len(a)):
...     print(i, a[i])
...

break

>>> for n in range(2, 10):
...     for x in range(2, n):
...         if n % x == 0:
...             print(n, 'equals', x, '*', n//x)
...             break
...     else:
...         # loop fell through without finding a factor
...         print(n, 'is a prime number')
...

continue

>>> for num in range(2, 10):
...     if num % 2 == 0:
...         print("Found an even number", num)
...         continue
...     print("Found an odd number", num)
...

Functions

>>> def fib(n):    # write Fibonacci series up to n
...     """Print a Fibonacci series up to n."""
...     a, b = 0, 1
...     while a < n:
...         print(a, end=' ')
...         a, b = b, a+b
...     print()
...
>>> fib(2000)

Default Argument Values

def ask_ok(prompt, retries=4, reminder='Please try again!'):
    while True:
        ok = input(prompt)
        if ok in ('y', 'ye', 'yes'):
            return True
        if ok in ('n', 'no', 'nop', 'nope'):
            return False
        retries = retries - 1
        if retries < 0:
            raise ValueError('invalid user response')
        print(reminder)

This function can be called in several ways:

1. By giving only the mandatory argument:

   ask_ok('Do you really want to quit?')

2. By giving one of the optional arguments:

   ask_ok('OK to overwrite the file?', 2)

3. By giving all arguments:

   ask_ok('OK to overwrite the file?', 2, 'Come on, only yes or no!')

Further Reading

• https://docs.python.org/3/tutorial/introduction.html