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Text type str

Python strings

Strings in python are surrounded by either single quotation marks, or double quotation marks.
‘Eunice’ is the same as “Eunice”.

Multiline Strings assign a multiline string to a variable by using three quotes

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a = """AI, Mechine learning, Deep learning"""
print(a)
b = '''Linear regression, Polynomial regression, Ridge regression, Lasso regression, Logistic regression'''
print(b)

AI, Mechine learning, Deep learning
Linear regression, Polynomial regression, Ridge regression, Lasso regression, Logistic regression

Strings are Arrays
Strings are arrays of bytes representing unicode characters. We can loop through the characters in a string, with a for loop.

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a = "Hey, Eunice!"
print(a[0], a[8])
for x in "Eunice":
  print(x)

H i
E
u
n
i
c
e

Check String Length and Check string len(), in, if, not in

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a = "Hi, Harry!"
print(len(a))

txt = "The cutest shiba dog in the world is Harry!"
print("cutest" in txt)

if "cutest" in txt:
  print("Yes, 'cutest' is present.")

print("ugly" not in txt)

if "ugly" not in txt:
  print("No, 'ugly' is NOT present.")

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True
Yes, ‘cutest’ is present.
True
No, ‘ugly’ is NOT present.

Slicing Strings

We can return a range of characters by using the slice syntax. Specify the start index and the end index, separated by a colon, to return a part of the string.

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# Get the characters from position 2 to position 5 (not included)
b = "Hello, Harry!"
print(b[3:5])
# By leaving out the start index, the range will start at the first character
print(b[:5])
# By leaving out the end index, the range will go to the end
print(b[3:])
# Use negative indexes to start the slice from the end of the string
print(b[-5:-2])

llo
Hello
llo, Harry!
arr

Modify Strings

Python has a set of built-in methods that you can use on strings.
upper(), lower(), strip(), replace() split()

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a = "Hello, Harry!"
print(a.upper())
print(a.lower())
print(a.strip()) # returns "Hello, World!"
print(a.replace("H", "J"))
print(a.split(",")) # returns ['Hello', ' World!']

HELLO, HARRY!
hello, harry!
Hello, Harry!
Jello, Jarry!
[‘Hello’, ‘ Harry!’]

Concatenation

To concatenate, or combine, two strings you can use the + operator.

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a = "Hello"
b = "Harry"
c = a + b # Merge variable a with variable b into variable c
print(c)
d = a + " " + b # To add a space between them, add a " "
print(d)

HelloHarry
Hello Harry

Format format()

If we want to combine strings and numbers, we can use format() and {}.

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age = 3
txt = "This is shiba Harry, and he is {} years old."
print(txt.format(age))

quantity = 3
item = "chocolate cakes"
price = 900
myorder = "I want {} pieces of {} for {} dollars."
print(myorder.format(quantity, item, price))

myorder = "I want to pay {2} dollars for {0} pieces of {1}."
print(myorder.format(quantity, item, price))

This is shiba Harry, and he is 3 years old.
I want 3 pieces of chocolate cakes for 900 dollars.
I want to pay 900 dollars for 3 pieces of chocolate cakes.

Escape Character

To insert characters that are illegal in a string, use an escape character.
An escape character is a backslash \ followed by the character you want to insert.

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txt = "We are the so-called \"Vikings\" from the north."
Code Result
' Single Quote
\ Backslash
\n New Line
\r Carriage Return
\t Tab
\b Backspace
\f Form Feed
\ooo Octal value
\xhh Hex value

String Method

Python has a set of built-in methods that you can use on strings.
Note: All string methods return new values. They do not change the original string.

Method Description
capitalize() Converts the first character to upper case
casefold() Converts string into lower case
center() Returns a centered string
count() Returns the number of times a specified value occurs in a string
encode() Returns an encoded version of the string
endswith() Returns true if the string ends with the specified value
expandtabs() Sets the tab size of the string
find() Searches the string for a specified value and returns the position of where it was found
format() Formats specified values in a string
format_map() Formats specified values in a string
index() Searches the string for a specified value and returns the position of where it was found
isalnum() Returns True if all characters in the string are alphanumeric
isalpha() Returns True if all characters in the string are in the alphabet
isdecimal() Returns True if all characters in the string are decimals
isdigit() Returns True if all characters in the string are digits
isidentifier() Returns True if the string is an identifier
islower() Returns True if all characters in the string are lower case
isnumeric() Returns True if all characters in the string are numeric
isprintable() Returns True if all characters in the string are printable
isspace() Returns True if all characters in the string are whitespaces
istitle() Returns True if the string follows the rules of a title
isupper() Returns True if all characters in the string are upper case
join() Joins the elements of an iterable to the end of the string
ljust() Returns a left justified version of the string
lower() Converts a string into lower case
lstrip() Returns a left trim version of the string
maketrans() Returns a translation table to be used in translations
partition() Returns a tuple where the string is parted into three parts
replace() Returns a string where a specified value is replaced with a specified value
rfind() Searches the string for a specified value and returns the last position of where it was found
rindex() Searches the string for a specified value and returns the last position of where it was found
rjust() Returns a right justified version of the string
rpartition() Returns a tuple where the string is parted into three parts
rsplit() Splits the string at the specified separator, and returns a list
rstrip() Returns a right trim version of the string
split() Splits the string at the specified separator, and returns a list
splitlines() Splits the string at line breaks and returns a list
startswith() Returns true if the string starts with the specified value
strip() Returns a trimmed version of the string
swapcase() Swaps cases, lower case becomes upper case and vice versa
title() Converts the first character of each word to upper case
translate() Returns a translated string
upper() Converts a string into upper case
zfill() Fills the string with a specified number of 0 values at the beginning