Strings

Complete Python Course ( Python for beginners)

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Python’s standard library is very extensive, offering a wide range of facilities. The library contains built-in modules (written in C) that provide access to system functionality such as file I/O that would otherwise be inaccessible to Python programmers, as well as modules written in Python that provide standardized solutions for many problems that occur in everyday programming

In this tutorial, we will learn everything which a beginner and a DevOps engineer should know in Python. We will cover the basic definition of python and some brilliant examples which will be enough to get you started with Python and for sure you will love it.

Table of content

  1. What is Python?
  2. Prerequisites
  3. Python Keywords
    • Python Numbers
    • Python Strings
    • Python Tuple
    • Python Lists
    • Python Dictionary
    • Python Sets
  4. Python variables
  5. Python Built-in functions
  6. Python Handling Exceptions
  7. Python Functions
  8. Python Searching
  9. Conclusion

Python String

Python strings are a collection of characters surrounded by quotes ” “. There are different ways in which strings are declared such as:

  1. str() – In this method you decalre the characters or words or data inside the double quotes.
  1. Directly calling it in quotes – “Hello, this is method2 to display string”
  1. Template strings – Template strings are designed to offer a simple string substitution mechanism. These built-in methods work for tasks where simple word substitutions are necessary.
from string import Template
new_value = Template("$a b c d")       #  a will be substituted here
x = new_value.substitute(a = "Automation")
y = new_value.substitute(a = "Automate")
print(x,y)

Some Tricky Examples of declaring string

Input String

print('This is my string 1')   # Correct String
print("This is my string 2")   # Correct String


# Examples of Special characters inside the String such as quotes

# print('Hello's Everyone')  # Incorrect Statement
print('Hello\'s Everyone')   # Correct Statement after using escape (To insert characters that are illegal in a string, use an escape character. )
print("Hello's Everyone")    # Correct Statement enclose within double quotes
print('Hello "shanky')       # Correct Statement 
print('Hello "shanky"')      # Correct Statement
# print("Hello "S"shanky") # Incorrect Statement
print("Hello ""shanky")  

# No need to Escape if using triple quotes but proper use of triple quotes
print(''''This is not a string "''')
print('''Hello" how' are"" u " I am " f'ine'r''')
print('''''Hello" how' are"" u " I am " f'ine'r''')
print("""'''''Hello" how' are"" u " I am " f'ine'r""")

Output String

This is my string 1
This is my string 2
Hello's Everyone
Hello's Everyone
Hello "shanky
Hello "shanky"
Hello shanky
'This is not a string "
Hello" how' are"" u " I am " f'ine'r
''Hello" how' are"" u " I am " f'ine'r
'''''Hello" how' are"" u " I am " f'ine'r

Python Tuple

Tuples: Tuples are immutable ordered sequence of items that cannot be modified. The items of a tuple are arbitrary objects and may be of different types and allow duplicate values. For Example

# 10,20,30,30 are fixed at respective index 0,1,2,3 positions 
(10,20,30,30) or (3.14,5.14,6.14)

Python Dictionaries

Dictionary are written as key:value pair , where key is an expression giving the item’s key and value is an expression giving the item’s value. A dictionary is a collection which is ordered*, changeable and does not allow duplicates.

# Dictionary with three items where x,y and z are keys.
# where x,y and z have 42, 3.14 and 7 as the values.
{'x':42, 'y':3.14, 'z':7}

Python Sets

Sets: Set stores multiple items in a single variable. It contains unordered and unindexed data. Sets cannot have two items with the same value. 

{"apple", "banana", "cherry"}
Data typesMutable or Immutable
StringImmutable (Cannot be modified)
TuplesImmutable (Cannot be modified)
IntegersImmutable (Cannot be modified)
ListMutable (Can be modified)
SetsMutable (Can be modified)
Floating pointImmutable (Cannot be modified)
DictionariesMutable (Can be modified)

Python variables

Variables are stored as a information it could be number , symbol , name etc. which are used to be referenced. Lets see some of the examples of Python variables.

  • There are few points one must remember when using variables such as
    • Variables cannot start with digits
    • Spaces are not allowed in variables.
    • Avoid using Python keywords

Example 1:

  • In below example var is a variable and value of var is this is a variable 
var="this is a variable" # Defining the variable
print(var)    # Printing the value of variable

Example 2:

  • In below example we are declaring three variable.
    • first_word and second_word are storing the values
    • add_words is substituting the variables with values
first_word="hello"
second_word="devops"
add_words=f"{first_word}{second_word}"
print(add_words)
  • If you wish to print words in different line then use "\n" as below
first_word="hello"
second_word="devops"
add_words=f"{first_word}\n{second_word}"
print(add_words)

Dictionary

In simple words these are key value pairs where keys can be number, string or custom object. Dictionary are represented in key value pairs separated by comma within curly braces.

map = {'key-1': 'value-1', 'key-2': 'value-2'}
  • You can access the particular key using following way
map['key-1']

Lets see an example to access values using get() method

my_dictionary = {'key-1': 'value-1', 'key-2': 'value-2'}
my_dictionary.get('key-1')    # It will print value of key-1 which is value-1
print(my_dictionary.values()) # It will print values of each key
print(my_dictionary.keys())   # It will print keys of each value
my_dictionary.get('key-3')    # It will not print anything as key-3 is missing

Python Built-in functions

There are various single line command which are already embedded in python library and those are known as built in functions. You invoke a function by typing the function name, followed by parentheses.

  • To check the Python version on windows or Linux machine run the following command.
python3 --version
  • To print the output of a program , use the print command.
print("Hello Devops")
  • To generate a list of number through a range built-in function run the following command.
list(range(0,10))

Handling Exceptions

Exceptions are error which causes a program to stop if not handled properly. There are many built-in exceptions, such as IOError, KeyError, and ImportError. Lets see a simple example below.

  • Here we defined a list of characters and stored it in a variable devops
  • Now, while true indicated that till the ,condition is true it will execute the try block.
  • .pop() is built in method to remove each item one by one.
  • Now in our case as soon as all the characters are removed then except block catches the IndexError and prints the message.
devops = ['d','e','v','o','p','s']
 
while True:
    try:
        devop = devops.pop()
        print(devop)
    except IndexError as e:
        print("I think I did lot of pop ")
        print(e)
        break
 
Output:
 
s
p
o
v
e
d
I think I did lot of pop
pop from empty list

Python Functions

Earlier in this tutorial we have already seen that there are numerous built in function and some of them you used above. But you can define and create your own functions. Lets see the syntax of function.

def <FUNCTION NAME>(<PARAMETERS>):
    <CODE BLOCK>
<FUNCTION NAME>(<ARGUMENTS>)

Lets look at some of the Python functions examples

EXAMPLE 1

  • Here each argument use order of arguments to assign value which is also known as positional argument.
  • a and b variables are parameters which are required to run the function
  • 1 and 2 are arguments which are used to pass the value to the function ( arguments are piece of information that’s passed from a function call to a function)
def my_function(a,b):
  print(f" value of a is {a}")
  print(f" value of b is {b}")
my_function(1, 2)

EXAMPLE 2:

  • With keyword arguments, assign each argument a default value:
def my_function(a=3,b=4):
  print(f" value of a is {a}")
  print(f" value of b is {b}")
my_function()

EXAMPLE 3

Passing arbitrary number of arguments. When you are not sure about the number of parameters to be passed then we call it as arbitrary. Lets look at an example

  • Find the Even in the string

mylist = []
def myfunc(*args):      #  args is to take any number of arguments together in myfunc
    for item in args:
        if int(item)%2 == 0:
            mylist.append(item)
    print(mylist)
myfunc(5,6,7,8,9)

EXAMPLE 4

  • IF LOOP: Find the least among two numbers if both numbers are even else return greater among both the numbers

def two_of_less(a,b):    # Defining the Function where a and b variables are parameters
    if a%2==0 and b%2==0:
      print(min(a,b))       # using built in function min()
    if a%2==1 or b%2==1:
      print(max(a,b))       # using built in function max()
two_of_less(2,4)

EXAMPLE 5

  • Write a function takes a two-word string and returns True if both words begin with same letter

def check(a):
    m = a.split()
    if m[0][0] == m[1][0] :
     print("Both the Words in the string starts with same letter")
    else:
     print("Both the Words in the string don't start with same letter")    
check('devops Engineer')

Python Searching

The need to match patterns in strings comes up again and again. You could be looking for an identifier in a log file or checking user input for keywords or a myriad of other cases.

Regular expressions use a string of characters to define search patterns. The Python re package offers regular expression operations similar to those found in Perl.

Lets look at example which will give you overall picture of in built functions which we can use with re module.

  • You can use the re.search function, which returns a re.Match object only if there is a match.
import re
import datetime
 
name_list = '''Ezra Sharma <esharma@automateinfra.com>,
   ...: Rostam Bat   <rostam@automateinfra.com>,
   ...: Chris Taylor <ctaylor@automateinfra.com,
   ...: Bobbi Baio <bbaio@automateinfra.com'''
 
# Some commonly used ones are \w, which is equivalent to [a-zA-Z0-9_] and \d, which is equivalent to [0-9]. 
# You can use the + modifier to match for multiple characters:
 
print(re.search(r'Rostam', name_list))
print(re.search('[RB]obb[yi]',  name_list))
print(re.search(r'Chr[a-z][a-z]', name_list))
print(re.search(r'[A-Za-z]+', name_list))
print(re.search(r'[A-Za-z]{5}', name_list))
print(re.search(r'[A-Za-z]{7}', name_list))
print(re.search(r'[A-Za-z]+@[a-z]+\.[a-z]+', name_list))
print(re.search(r'\w+', name_list))
print(re.search(r'\w+\@\w+\.\w+', name_list))
print(re.search(r'(\w+)\@(\w+)\.(\w+)', name_list))

OUTPUT 

<re.Match object; span=(49, 55), match='Rostam'>
<re.Match object; span=(147, 152), match='Bobbi'>
<re.Match object; span=(98, 103), match='Chris'>
<re.Match object; span=(0, 4), match='Ezra'>
<re.Match object; span=(5, 10), match='Sharm'>
<re.Match object; span=(13, 20), match='esharma'>
<re.Match object; span=(13, 38), match='esharma@automateinfra.com'>
<re.Match object; span=(0, 4), match='Ezra'>
<re.Match object; span=(13, 38), match='esharma@automateinfra.com'>
<re.Match object; span=(13, 38), match='esharma@automateinfra.com'>
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