Strings in python

How to define a string in python?

There are 4 different ways of doing that, you can use single quotes, double quotes, triple quotes, and triple-double quotes!!!
Example:

s = "Traditional way of defining a string"
s1 = 'Easier way of defining the string'
s2 = '''This is another
way of defining a string, in paragraphs'''
s3 = """
"roses are red, 
violets are blue,
if you like forking, 
then you will like Github too."
 - this entire lame poem is also a string, quite long, but a string!
"""
print(s,s1,s2,s3,sep='\n')

Output

Traditional way of defining a string
Easier way of defining the string
This is another
way of defining a string, in paragraphs

"roses are red, 
violets are blue,
if you like forking, 
then you will like Github too."
- this entire lame poem is also a string, quite long, but a string!

String Indexing and Slicing

Alt text You can access the characters of the string using +ve or -ve indices.

Example:

s = 'chocolate'
print(f'First character: {s[0]}') # this is f-sting**
print(f'Last character: {s[-1]}') 
# s[start index: end index :steps]
#  Using this you can slice a part of a string
print(f'First 3 character: {s[:3]}') 
print(f'Last 3 character: {s[-3:]}')

s[:3] is same as s[0:3] so you needn't write the starting index.

Output

First character: c

Last character: e

First 3 character: cho

Last 3 character: ate

Now if you want to reverse the string, you can do that using slicing. Just set steps to -1

print(f'Reverse String is : {s[::-1]}')

Output

Reverse String is : etalocohc

If you want to take out the middle portion of chocolate then use this:

s = 'chocolate'
print(f'Middle Portion : {s[3:7]}')

Output

Middle Portion : cola

And that's how you extract cola from chocolate

String concatenation

Want to concatenate multiple strings? LOL! Piece of . Just use the + operator. Like This:

s = "first Name" + "middle name" + 'Last name'
print(s)

Output

first Nameiddle nameLast name

To concatenate same string multiple times use *:

s = 'LOL'*5
print(s)

Output

LOLLOLLOLLOLLOL

Manipulate your strings:

.replace()

Consider this example:

s = "Angela is my girlfriend"

It's been ages with her, she has taken me for granted so I want to replace her. I don't know about real life, but this is easy in python.

s = s.replace('Angela','Anjali') 
# .replace('old substring','new substring')
print(s)

Output

Anjali is my girlfriend

.count()

Returns the frequency of a substring

s ="mi go, mi eat, amigo come, mi again go"
print('Considering the whole string',s.count('mi'),sep='\t')
print(f'Considering only "{s[13:25]}"',s.count('mi',13,25),sep='\t')

Output

Considering the whole string 4

Considering only ", amigo come" 1

.lower(), .upper(), .swapcase() & .capitalize()

s ="meRRy XmAs"
print(s,s.lower(),s.upper(),s.capitalize(),s.swapcase(),s.title(),sep='\n')

Output

meRRy XmAs | original string

merry xmas | output of lower() | all letters -> lowercase

MERRY XMAS | output of upper() | all letters -> uppercase

Merry xmas | output of captalize() | only capitalizes the initials of the first word of a string

MErrY xMaS | output of swapcase() | self-explanatory

Merry Xmas | output of title() | capitalizes all the initials

.islower(), .isupper(), .isdigit()

print("UPPER".isupper(),'uPPer'.isupper())
        # True          False

print('loWer'.islower(),'lower'.islower())
        # False             True

print('lol'.isdigit(),'92'.isdigit(),'3.4'.isdigit(),'/*-'.isdigit())
#       False               True            False       False

.isspace(), .istitle(), .isdecimal()

print('   '.isspace(),'    s   '.isspace())
        # True               False

print('1.2'.isdecimal(),'12'.isdecimal(),'.12'.isdecimal())
        # False          True                False

print('Title Shitel'.istitle(),'title shitel'.istitle(),'titlE'.istitle())
#        True                    False                   False

.isnumeric(), .isalpha(), .isalnum()

print('sOmethIng'.isalpha(),'anglepriya420'.isalpha())
                # True           False

print('12'.isnumeric(),'1.2'.isnumeric(),'numeric'.isnumeric())
            # True               False       False

print('aasd233'.isalnum(),'123'.isalnum(),'assert'.isalnum(),'1s#'.isalnum(),'spa ce'.isalnum())
        # True              True          True                     False       False

.endswith(), .startswith()

filename = 'unnecessary.csv'
print(filename.endswith('.csv'),filename.endswith('.CSV'))

Output

True False

print('Miss Hitler'.startswith('Miss'))
            # True
print('Miss Hitler'.startswith('miss'))
            # False
print('Miss Hitler'.lower().startswith('miss'))
            # True

.split(), .join()

split() method splits the string on the basis of a delimiter, provided by the user. returns a list of words.

By default the delemiter is set to ' '.

Example 1

s = 'This is a string'
print(s)
s = s.split()
print(s)

Output

This is a string

['This', 'is', 'a', 'string']

Example 2

s = 'name,age,sex,roll,num'
print(s)
s = s.split(',')
print(s)

Output

name,age,sex,roll,num

['name', 'age', 'sex', 'roll', 'num']

.join() method concatenate all strings of a given iterable( list, tuples,.etc)

Example:

l = ['name', 'age', 'sex', 'roll', 'num']
print(' '.join(l))

Output

name age sex roll num

REGEX

Used to search for a specific pattern in a text.

[]{}()\^$|?*+ are few characters which we need to expace using a \ as a prefix before search for these.

. matches all characters except newline

\d matches all the digits whereas \D matches everthing but digits.

\w = word | \W = Not a word

\s = space | \S = not a space

\b = word boundary | \B = Not a word boundary

^ = Start of a string

$ = end of a string

* = 0 or more

+ = 1 or more

? = 0 or one match

{5} = exact number of match

{min,max} = range of numbers