Learn Python Fundamental in 30 Days — Day 3(Strings)

Strings is just a sequence of characters letters,special characters,space,digits

We can use single/double quote to represent a string

>>> x = “hello”
>>> x
‘hello’
>>> x = ‘hello’
>>> x
‘hello’

Reason for using single vs double quote in a string

>>> ‘I don’t know you’
 File “<stdin>”, line 1
 ‘I don’t know you’
 ^
SyntaxError: invalid syntax
>>> “I don’t know you”
“I don’t know you”

Operations on Strings

To determine the length of string

>>> len(“hello”)
5

# Concatenation is done using + operator(or in other words we can say, we have overloaded it)

>>> "hello " + "world"
'hello world'

# Successive Concatenation on string

>>> x = "hello "
>>> x * 3
'hello hello hello '

# Indexing on string(Indexing start with zero not one)

>>> x[0]
‘h’

# To get the last element

>>> x[-1]
'o'

# Try to get something out of range

>>> x[5]
Traceback (most recent call last):
File “<stdin>”, line 1, in <module>
IndexError: string index out of range

# We can slice the string

>>> x[0:3]
'hel'
# OR
>>> x[:3]
'hel'
# To grab everything
>>> x[:]
'hello'

# We can also use join() to join string

>>> “-”.join([“hello”,”how”,”are”,”you”])
‘hello-how-are-you’

# Then we can call split() to divide a string into a list(Without an argument split() divides on whitespace)

>>> y
‘hello-how-are-you’
>>> y.split(“-”)
[‘hello’, ‘how’, ‘are’, ‘you’]
# Split by specific element
>>> x = "hello world"
>>> x.split('w')
['hello ', 'orld']

#Partition() method divides a string into three, around a separator(prefix,separator,suffix)

>>> "hastalevista".partition("le")
('hasta', 'le', 'vista')

# As it return a tuple it’s useful to destructure the result

>>> x,y,z = “hastalevista”.partition(“le”)
>>> x
‘hasta’
>>> y
‘le’
>>> z
‘vista’

# We can _ as a dummy name for the separator

>>> a,_,b = "hello-world".partition("-")
>>> a
'hello'
>>> b
'world'
>>> _
'-'

NOTE the major difference between split and partition

# Partition based on first occurrence and return a seperator
>>> x.partition(‘l’)
(‘he’, ‘l’, ‘lo’)
# It split the string on every occurrence of 'l'
>>> x.split(‘l’)
[‘he’, ‘’, ‘o’]

# Format() is used to insert values into strings,replacement fields delimited by { and }

>>> "My name is {0} and my age is {1}".format("Prashant",33)
'My name is Prashant and my age is 33'

String Methods

Objects in Python usually have built-in methods. These methods are functions inside the object that can perform actions or command on the object itself

• Upper case a string

>>> x
‘hello’
>>> x.upper()
‘HELLO’

• Lower case a string

>>> x.lower()
‘hello’

• Capitalize first word in string

>>> x.capitalize()
‘Hello world’

• Count how many o in string

>>> x.count(“o”)
2

• Location of first occurrence of o

>>> x.find(“o”)
4

• isalnum() will return True if all characters in x are alphanumeric

>>> x.isalnum()
True

• isalpha() wil return True if all characters in x are alphabetic

>>> x.isalpha()
True

• islower() will return True if all cased characters in x are lowercase and there is at least one cased character in x, False otherwise.

>>> x.islower()
True

• To check if strings ends with particular character

>>> x.endswith(‘o’)
True

NOTE:

Please be careful with these type of operations

• Strings are immutable: Once it’s created we can’t change it

>>> x
‘hello’
>>> x[0] = ‘y’
Traceback (most recent call last):
 File “<stdin>”, line 1, in <module>
TypeError: ‘str’ object does not support item assignment

However you can do it like this

>>> x = “y” + x[1:]
>>> x
‘yello’

• Multiply string with string with lead to an error

>>> “1” * “ab”
Traceback (most recent call last):
File “<stdin>”, line 1, in <module>
TypeError: can’t multiply sequence by non-int of type ‘str’

• Out of range error as len starts with zero

>>> x = "hello"
>>> len(x)
5
>>> x[len(x)]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
IndexError: string index out of range

• Case matter in Python(hello and HELLO are not equal)

>>> x
'hello'
>>> x == "HELLO"
False

• Some tricky stuff ,print everything except last character

>>> x[:-1]
'hell'

• Use of step(print with an increment of 2)

>>> x[0:4:2]
'hl'

• Famous interview question(Reverse a string ;-))

>>> x[::-1]
'olleh'

Exercise

What is the output of:

1. “a” + “bc”
2. What is the difference in output of “ab” * 2 vs “ab” * “2”
3. What is the difference in output of “abcde”[3] vs “abcde”[5]
4. What is the difference in output of “abcde”[0:2] vs “abcde”[:2] vs “abcde”[2:]
5. If x = “hello” ,what is len(x) and x(len(x))

So this end of Day3, In case if you are facing any issue, this is the link to Python Slack channel https://devops-myworld.slack.com

Please send me your details

• First name
• Last name
• Email address

to devops.everyday.challenge@gmail.com, so that I will add you to this slack channel

HAPPY CODING!!