Strings		Variables		Lists		Tuples		Dictionary
Control		Function		Files		Exceptions
OOP		Algorithm		Data Structure		back

---

String

• data type that’s used to represent a piece of text. 
• either double quotes or single quotes. 
• strings are immutable.

name = "Mike"

pet = ""# called an empty string
pet = 'looooooooooooooooooooooooong cat'

String operations	what it does
len(string)	Returns the length of the string
for character in string	Iterates over each character in the string
if substring in string	Checks whether the substring is part of the string
string[i]	Accesses the character at index i of the string, starting at zero
string[i:j]	Accesses the substring starting at index i, ending at index j-1. If i is omitted, it’s 0 by default. If j is omitted, it’s len(string) by default.

Concatenating

• using the plus sign to build longer strings.

len function

• number of characters contained in the string. 

Example Modify the double_word function so that it returns the same word repeated twice, followed by the length of the new doubled word. => double_word(“hello”) should return hellohello10.

def double_word(word):
	return word + word + str(len(word) * 2)

    return

print(double_word("hello")) 
# Should return hellohello10
print(double_word("abc"))   
# Should return abcabc6
print(double_word(""))      
# Should return 0

substring in string

pets = "Cats & Dogs"
"Dragons" in pets
	False

String Indexing and Slicing

• to access just a specific character or characters? 
• to access a portion of a string, called a slice or a substring
• using square brackets and the location, or index, of the character you want to access.

name = "Mike"
print(name[2])
# OUTPUT
# k

fruit = "Mangosteen"
fruit[1:4]
#OUTPUT
'ang'

fruit[:5]
#OUTPUT
'Mango'

fruit = "Pineapple"
print(fruit[:4])
# OUTOUT
Pine
print(fruit[4:])
# OUTOUT
apple

negative indexes. 

text = "Random staring with a lot of characters"
print(text[-1])
print(text[-2])
OUTPUT
s
r

• don’t know the length of the string (it doesn’t matter). 
• Negative indexes lets us access the positions in the string starting from the last. 
• If you try to access an index that’s larger than the length of your string, you’ll get an IndexError.

Changing a character in a string

• strings in Python are immutable. => create a new string based on the old one.
• You don’t replace a string, but create a new variable.

message = "A kong string with a silly typo"
new_message = message[0:2] + 'l' + message[3:]
print(new_message)
A long string with a silly typo

index() Method Find character to change

• how are we supposed to know which character to change? 
• returns just the first position that matches.

pets = "Cats & Dogs"
pets.index("&")
# OUTPUT
5

String methods	what it does
string.lower() / string.upper()	Returns a copy of the string with all lower / upper case characters
string.lstrip() / string.rstrip() / string.strip()	Returns a copy of the string without left / right / left or right whitespace
string.count(substring)	Returns the number of times substring is present in the string
string.isnumeric()	Returns True if there are only numeric characters in the string. If not, returns False.
string.isalpha()	Returns True if there are only alphabetic characters in the string. If not, returns False.
string.split() / string.split(delimiter)	Returns a list of substrings that were separated by whitespace / delimiter
string.replace(old, new)	Returns a new string where all occurrences of old have been replaced by new.
delimiter.join(list of strings)	Returns a new string with all the strings joined by the delimiter

• string method lower/string.upper() can be super handy when checking user input, since someone might type in all lowercase, all uppercase, or even a mixture of cases.
• strip method to remove surrounding whitespace from a string. Whitespace includes spaces, tabs, and newline characters.
• lstrip and rstrip methods to remove whitespace only from the left or the right side of the string, respectively.
• count() method for finding out
  • how many characters appear in a string,
  • counting the number of times a certain word appears in a sentence or paragraph.
• endswith() method: to check if a string ends with a given substring. This will return True if the substring is found at the end of the string, and False if not.

"Forest".endswidth("rest")
#OUTPUT
True

txt = "Hello, welcome to my world."
x = txt.startswith("Hello")
print(x)

• The isnumeric method can check if a string is composed of only numbers. If the string contains only numbers, this method will return True. We can use this to check if a string contains numbers before passing the string to the int() function to convert it to an integer, avoiding an error. Useful!

string.lower() method

answer = 'YES'
	if answer.lower() =="yes":
		print("User said yes")

docs.python.org

---

Formatting

w3schools

%-formatting

>>> name = "Eric"
>>> "Hello, %s." % name
'Hello, Eric.'

str.format()

>>> person = {'name': 'Eric', 'age': 74}
>>> "Hello, {name}. You are {age}.".format(name=person['name'], age=person['age'])
'Hello, Eric. You are 74.'

f-Strings

>>> name = "Eric"
>>> age = 74
>>> f"Hello, {name}. You are {age}."
'Hello, Eric. You are 74.'

>>> name = "Eric"
>>> profession = "comedian"
>>> affiliation = "Monty Python"
>>> message = (
...     f"Hi {name}. "
...     f"You are a {profession}. "
...     f"You were in {affiliation}."
... )
>>> message
'Hi Eric. You are a comedian. You were in Monty Python.'

print() function

# basic print() function
values=["one", "two", "three", "four", "five"]
print(*values)

# use the 'sep' argument to control the separator between values:
print(*values, sep=' -- ')

# use the 'end' argument to control the line ending characters
# let's auto-print the current line number along with each item!
for i in range(0, len(values)):
    print(values[i], end=f" [line: {str(i+1)}]\n")

# you can even redirect print() output to a file:
newfile = open("output.txt","w")
print(*values, sep=' -- ', file=newfile, flush=True)
newfile.close()

docs.python