Python Strings

Python String Datatype

A string literal is simply a list of characters (textual data) in sequence surrounded by quotes.
A character can be anything like numbers, backslash or letters and can also have space.
For example,"easy"is a string.
It is a four character long with each characters in sequence "e", "a", "s", "y"
We can assign the same string to a variable as follows

mystring = "easy" # create a 4 character string objects and assign it to name "mystring"

mystring is the variable name to which the string object is assigned.
There are fours ways you can declare a string literal (or create a string object) in Python i.e. single quotes ('), double quotes ("), triple double quotes (""") and triple single quotes (''')
Example:

string1 = 'It is a single quoted string'
string2 = "It is a double quoted string"
string3 = """It is a triple double quoted string"""
string4 = '''It is a triple single quoted string'''
multiline_string1 = """
This is a
sting in multiple lines
"""
multiline_string2 = '''
This is a
sting in multiple lines
'''
unicode_string = u'e\xc4sy'
print(type(string1))
print(type(unicode_string))

<class 'str'>
<class 'str'>

type() - is a built-in function which returns the type to which the object belongs. Refer to https://docs.python.org/3.7/library/functions.html#type
multilinestring1 and multilinestring2 are multi-line string literals. We can write multiple line texts/string using triple double quotes (""") and triple single quotes (''')
unicodestring is unicode string literal.

Indexing in Python String

The characters are stored in order or sequence in the memory with a particular position assigned to each of the character.
The positions or the offsets are known as index.
Example:

mystring = "easy" # create a 4 character string objects and assign it to name "mystring"

As "e" is at index 0 we can retrieve and print "e" using name mystring as follows

print(mystring[0])

e

To retrieve "a" and others

print(mystring[1])
print(mystring[2])
print(mystring[3])

a
s
y

Negative Index

we can also index backward. The above positive indexes from 0, 1, 2 and so on -count form left to right
The negative index count from right to left starting with -1 e.g. -1, -2, -3.
So from the previous example mystring = "easy", if we want to retrieve "a" using mystring and negative index we can write

print(mystring[-3])  # is same as mystring[1]

a

So the value at 1 is same as -3 and 0 is as index -4

Slicing

We can also extract a portion of a string using indexes know as slicing.
The syntax is

variable_name[I:J] # Gives everything in variable_name from I to J, but inot including J

Example:

print(mystring[1:3])

as

So it extracts the string from offset/index 1 to 2 (Not including 3)

Python String Operators

>>> string1 = "py"
>>> string2 = "thon"
>>> string1 + string2
'python'

>>> str_1 = "Python"
>>> str_1 * 3
'PythonPythonPython'

>>> print('thi \nis ')
thi
is
>>> print(r'thi \nis ')
thi \nis
>>> print(R'thi \nis ')
thi \nis

>>> str_1 = "Python"
>>> "th" in str_1
True

>>> str_1 = "Python"
>>> "a" not in str_1
True
>>> "on" not in str_1
False

>>> str_1 = "Python %s easy" % ('is')
>>> str_1
'Python is easy'
>>> str_2 = 'Today is %dth Nov' % 14
>>> str_2
'Today is 14th Nov'

>>> str_1 = "Python"
>>> str_1[2]
't'

>>> str_1 = "Python"
>>> str_1[2:4]
'th'

Python String methods

>> string1 = "pythoneasy is python website"
>> string1.count('python')
2

>> string1 = "pythoneasy is python website"
>> string1.find('on')
4

>>> string1 = "python is easy"
>>> string1.upper()
'PYTHON IS EASY'

>>> string1 = "PYTHON IS EASY"
>>> string1.lower()
'python is easy'

>>> string1 = "Python Is Easy"
>>> string1.swapcase()
'pYTHON iS eASY'

>>> string1 = "python is easy"
>>> string1.title()
'Python Is Easy'

>>> phrase = 'lexical semantics'
>>> phrase.capitalize()
'Lexical semantics'

>>> string1 = "      python is easy          "
>>> string1
'      python is easy          '
>>> string1.strip()
'python is easy'

>>> list_1 = ['python', 'is', 'easy']
>>> ''.join(list_1)
'pythoniseasy'
>>> ' '.join(list_1)
'python is easy'
>>> print('\n'.join(list_1))
python
is
easy
>>> print('\t'.join(list_1))
python  is      easy

>>> string_1 = ' 1  2   3  '
>>> string_1.split()
['1', '2', '3']
>>> string_1 = ' 1 in 2  in  3  '
>>> string_1.split('in')
[' 1 ', ' 2  ', '  3  ']