Chapter 4 Strings

A string is a sequence of characters, and it is one of the basic data types used to represent text.

Strings are enclosed in either single quotes (') or double quotes ("), and you can use either as long as the opening and closing quotes match. Here are some key characteristics and operations related to strings in Python:

0. Creating Strings

# Using single quotes
single_quoted_string = 'Hello, Python!'

# Using double quotes
double_quoted_string = "Hello, Python!"

# Triple-quoted strings for multiline strings
multiline_string = '''This is a
multiline string.'''

1. String Concatenation

first_name = "John"
last_name = "Doe"
full_name = first_name + " " + last_name

print(full_name)

## John Doe

2. String Indexing and Slicing

my_string = "Python"

# Indexing (0-based)
first_char = my_string[0]  # Result: 'P'

print(first_char)

## P

syntax: string_object[from : to : increment]

# Slicing
substring = my_string[1:4:1]  # Result: 'yth'
substring = my_string[1:4]  # Result: 'yth'

print(substring)

## yth

print(my_string[::2])

## Pto

4.0.0.1 String Methods:

# Length of a string
length = len(my_string)  # Result: 6

# Converting to uppercase and lowercase
uppercase_string = my_string.upper()
lowercase_string = my_string.lower()

# Finding a substring
index_of_th = my_string.find("th")  # Result: 2

# Replacing a substring
new_string = my_string.replace("on", "er")  # Result: 'Pyther'

upper() : strings to uppercase lower() : strings to lowercase capitalize() : strings to uppercase 1st letter

"Ohh! my life!".upper()

## 'OHH! MY LIFE!'

"OHH! MY LIFE!".lower()

## 'ohh! my life!'

"star".capitalize()

## 'Star'

"is it lowercase".islower()

## True

"IS IT UPPERCASE".isupper()

## True

replace method

replace(): to replace part of a string syntax: string.replace(oldvalue, newvalue, count)

query = '''
select all_columns 
from my_table
'''
new_query = query.replace("my_table", "new_table_name")

print(new_query)

## 
## select all_columns 
## from new_table_name

strip method

strip() method removes leading or trailing white-space

raw_text = "   my text   "

raw_text.strip()

## 'my text'

split method

split() method breaks a string by specified character.

split() method returns list type.

raw_text = "banana, apple, cherry"

alist = raw_text.split(",")

alist

## ['banana', ' apple', ' cherry']

there are some whitespce in the splitted elements in the list

alist[1].strip()

## 'apple'

4.0.0.2 String Formatting:

name = "Alice"
age = 25
formatted_string = f"My name is {name} and I am {age} years old."
# Result: 'My name is Alice and I am 25 years old.'

4.0.0.3 Escape Characters:

escaped_string = "This is a line.\nThis is a new line.\tThis is a tab."

print(escaped_string)

## This is a line.
## This is a new line.  This is a tab.

4.0.0.4 Raw Strings:

raw_string = r"This is a raw string \n\t No escape characters here."

print(raw_string)

## This is a raw string \n\t No escape characters here.

4.0.0.5 Membership and Operations:

# Checking membership
contains_py = 'py' in my_string  # Result: True

# String repetition
repeated_string = my_string * 3  # Result: 'PythonPythonPython'

Strings in Python are immutable, meaning once a string is created, you cannot modify its contents. Any operation that appears to modify a string actually creates a new string. Understanding these operations and methods is crucial for working effectively with strings in Python.

4.0.0.6 loop thru strings

my_txt = "life"

for i in my_txt:
  print(i.upper())

## L
## I
## F
## E

4.0.0.7 in/not in

check if a phrase is present in a string

my_txt = "life is good!"

print("good" in my_txt)

## True

if "good" in my_txt:
  print(my_txt)

## life is good!

if "bad" not in my_txt:
  print("'bad' is not in the text")

## 'bad' is not in the text