More about Strings

Dr Ian Cornelius

Hello

Learning Objectives:
1. Understand the extra functionality of strings in Python
2. Demonstrate the ability to use strings and their extra functions

Previously…

Last week you were introduced to the string data type
You learnt how to declare variable that consists of a string
- i.e. using a double (") quote, single (') quote or three double (""") or three single (''') quotes

More String Stuff! (1)

Strings are a Sequence

Strings in Python are considered to be an array of bytes that represent unicode characters
- this is because Python does not have a character data type
Therefore, each element of a string can be accessed by its index number

stringExample1 = "Hello 4061CEM"

stringExample1[1]

stringExample1[1] = e

More String Stuff! (2)

String Length

As aforementioned, a string is a sequence of characters you can find out the length of a string
- i.e. how many characters are in the string
You can find out the length of a string by using the len() function

stringExample1 = "Hello 4061CEM"

len(stringExample1)
len('Hello World')

len(stringExample1) = 13

len(‘Hello World’) = 11

More String Stuff! (3)

Finding a Substring

You have been introduced to membership operators, and these can be used to check for substrings inside a string
This is achieved using the in keyword
- you can also check whether a character or phrase is not in the string itself
- this is achieved using a combination of the not and in keywords (not in)

stringExample1 = "Hello 4061CEM"

"4061CEM" in stringExample1
"4063" in stringExample1
"4063" not in stringExample1

“4061CEM” in stringExample1 = True

“4063” in stringExample1 = False

“4063” not in stringExample1 = True

Modifying Strings (1)

Python consists of built-in methods that can be used to modify strings

Uppercase

Strings can be converted to all uppercase styling using the upper() method
- the method is called directly on the variable or string itself

stringExample1 = "hello 4061cem"

stringExample1.upper()
"hello 4061cem".upper()

stringExample1.upper() = HELLO 4061CEM

“hello 4061cem”.upper() = HELLO 4061CEM

Modifying Strings (2)

Lowercase

Strings can be converted to all lowercase styling using the lower() method
- the method is called directly on the variable or string itself

stringExample1 = "HELLO 4061CEM"

stringExample1.lower()
"hElLo 4061CeM".lower()

stringExample1.lower() = hello 4061cem

“hElLo 4061CeM”.lower() = hello 4061cem

Modifying Strings (3)

White-space Removal

Strings can be modified to remove white-space that may exist at the beginning or end of the string using the strip() method
- the method is called directly on the variable or string itself

stringExample1 = " Hello 4061CEM "

stringExample1.strip()
" hello 4061cem ".strip()

stringExample1.strip() = Hello 4061CEM

” Hello 4061CEM “.strip() = hello 4061cem

Modifying Strings (4)

Replacing a Substring

You can replace a substring in a string using the replace() keyword
- the method is called directly on the variable or string itself

stringExample1 = "Hello 4061CEM"

stringExample1.replace("4061", "4059")
"Hello 4061CEM".replace("4061", "4063")

stringExample1.replace(“4061”, “4059”) = Hello 4059CEM

“Hello 4061CEM”.replace(“4061”, “4063”) = Hello 4063CEM

Modifying Strings (5)

Merging Strings

Strings can be merged/joined/concatenated using the + operator
Unlike integers where it would sum the two variables, in a string it will join or concatenate the two variables together

stringExample1 = "4061"
stringExample2 = "CEM"

print("Welcome to " + stringExample1 + stringExample2)

Welcome to 4061CEM print(“Welcome to” + stringExample1 + stringExample2) = Welcome to 4061CEM

Modifying Strings (6)

Merging Strings and Other Data Types i

Merging strings together with a number cannot be achieved using the + operator
However, it can be done using the format() method
- the method will take passed arguments and format them into placeholders denoted by curly braces (“{}”)

intExample1 = 4061
stringExample1 = "CEM"

"{}{}".format(intExample1, stringExample1)

“{}{}”.format(intExample1, stringExample1) = 4061CEM

Modifying Strings (7)

Merging Strings and Other Data Types ii

You can also position arguments into a placeholder by using an index number

intExample1 = 4061
stringExample1 = "CEM"
stringExample2 = "Programming and Algorithms 1"

"{}{}: {}".format(intExample1, stringExample2, stringExample1)
"{0}{2}: {1}".format(intExample1, stringExample2, stringExample1)

“{}{}: {}”.format(intExample1, stringExample2, stringExample1) =

		 4061Programming and Algorithms 1: CEM

“{0}{2}: {1}”.format(intExample1, stringExample2, stringExample1) =

		 4061CEM: Programming and Algorithms 1

Formatting a String

This uses the f character at the beginning of a string declaration
Inside this string, variables can be used when enclosed by curly braces ({})

name = "Ian Cornelius"
age = 33

f"Hello {name} it is nice to meet you!"
f"Hello {name} it is nice to meet you! Your age is: {age}."

f”Hello {name} it is nice to meet you!” =

		 Hello Ian Cornelius it is nice to meet you!

f”Hello {name} it is nice to meet you! Your age is: {age}.” =

		 Hello Ian Cornelius it is nice to meet you! Your age is: 33.

Escape Characters

There are some characters that are considered illegal when being used in a string
- i.e. strings created with a double quote (") will not allow another double quote inside it
To use illegal characters in a string, you can escape them using the backslash symbol (\)

stringExample1 = "Hello 4061CEM, this is the "best" course."
# This will throw an error

stringExample2 = "Hello 4061CEM, this is the \"best\" course."
# This will not throw an error as the second set of double quotes have been escaped

stringExample3 = "Hello 4061CEM, this is the 'best' course."
stringExample4 = 'Hello 4061CEM, this is the "best" course.'

Goodbye

Questions?
- Post them in the Community Page on Aula
Contact Details:
- Dr Ian Cornelius, ab6459@coventry.ac.uk