Learning Python

22 Aug 2019

Contents

  1. Escaping
  2. Methods
  3. Sequence Operations
  4. Lists within Lists
  5. Referencing
  6. Tuple
  7. Logic
  8. Loops
  9. Dictionaries
  10. Functions

Learning Python

Python is a strongly typed language meaning that it uses types such as strings and integars.

Python is a object-oriented (OOP).

Python is also case sensitive so myName and myname are different from one another.

  • 10 - Decimal
  • 0b10 - Binary
  • 0o10 - Octal
  • 0x10 - Hexidecimal

Integer in Python 2 is limited to 32bits for anything greater we use Long (64bit).

Python 3 has those limits removed and can exceed 64bit, Long does not exist anymore.

Escaping

  • \n = New Line Break
  • \t = New Tab
  • \\ = Escape Backslash
  • type()
  • len()
  • [] = Offset
  • [6:10] = Slicing
  • [6:10:2] = Slicing with a step

Methods

  • .lower() = Change to lower case
  • .upper() = Change to upper case
  • .capitalize() = Change the first character to uppercase
  • .title() = First character in each word is upper
  • .swapcase() = swaps case
  • .center() = Centers text within a character limit
  • .startswith() = Checks and Returns a Boolean value
  • .endswith()
  • .strip() = Removes white space by default or any combination of specified characters
  • .lstrip() = Removes space on the Left side
  • .rstrip() = Removes space on the Right Side
  • .split() = Returns a list of words using a delimiter.
  • .join() =
  • .index() = First occurrence of
  • .count() = Number of occurrences
  • .find() = Returns the lowest index, if value is not found then a -1 is returned

Sequence Operations

  • x in s = Returns a true if s is equal to x
  • x not in s = Returns a true if s is not equal to x
    • = Concat

Lists within Lists

First List - routers_list = ['R1','R2','R3']

Second List - switches_list = ['S1','S2','S3']

Combined List - rs_list = [routers_list, switches_list]

Results In rs_list = [['R1','R2','R3'],['S1','S2','S3']]

Calling each item using rs_list[0] = ['R1','R2','R3']

Calliung each sub item rs_list[0][1] = 'R2'

Referencing

a = [1,2,3]

b = a

when a is changed so will b as its only referencing. you can use the .copy() method to create a copy of the list.

c = a.copy()

or you can c = list(a) which creates a copy of the list.

Tuple

Tuples are like a list but are immutable, cannot change after creation.

Create a tuple using tuple1 = ('R1','R2') or tuple2 = 'R1', 'R2'.

Logic

IF, ELSE statement

router = True

if router:
    print ('This is a router')
else:
    print ('This is not a router')

IF, ELIF, ELSE statement

device = '123'

if device == 'router':
    print ('Router found')
elif device == 'switch':
    print ('Switch found')
else:
    print ('Something else found')

Loops

WHILE loop

counter = 1

while counter < 5:
    print (counter)
    counter += 1

break will stop a loop, continue will skip the loop back.

optional else: at the end of a while loop if the loop ends normally (no break).

FOR loop

Useful for iterating through a list.

vendors = ['cisco', 'hpe']

for vendor in vendors:
    print ('Vendor is: ', vendor)

Comparing lists is easy with a sub IF statement.

vendors = ['cisco', 'hpe', 'ss']
approved_vendors = ['cisco', 'hpe']

for vendor in vendors:
	if vendor not in approved_vendors:
    	print ('Dodgy vendor is: ', vendor)

Dictionaries

Similar to lists (unordered), order doesn’t matter, no offset instead you use keys (keys must be unique).

Dictionaries are immutable.

Calling keys from a dictionary to retrieve its value.

 iosv_l2_s1 = {
     'device_type': 'cisco_ios',
     'ip': '192.168.1.10',
     'username': 'admin',
     'password': 'cisco',
 }

 iosv_l2_s1['username']

changing a value of a key

iosv_l2_s1['password'] = 'class'

adding an additional key

iosv_l2_s1['secret'] = 'cisco'

combining dictionaries using the .update() method.

iosv_extra = {
    'protocol': 'ssh',
    'login': 'local',
}

iosv_l2_s1.update(iosv_extra)

remove keys using the del

del iosv_extra['login']

clear a whole dictionary using the .clear() method

iosv_extra.clear()

Functions

Named modular code which can be reused.

Defining and calling a function

def functionName():
    print ('Hello')

functionName()

Function Arguments = functionName(Arg)

Named Keyword Arguments = removes confusion with positional arguments.

def functionName(username, password):
    return {
        'username': username,
        'password': password,
    }

functionName(username = 'admin', password = 'cisco')

functionName(password = 'cisco', username = 'admin')
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