COMP7004 - Systems Scripting

Lecture 17: More Python Strings and Copying to Clipboard

Dr. Vincent Emeakaroha

vincent.emeakaroha@mtu.ie

Semester 2, 2026

The startswith() and endswith()

String Methods

• These methods are handy in situations where you want to

check if a string sentence starts with or ends with a particular

word.

• The startswith() and endswith() methods return True if the

string value they are called on begins or ends (respectively)

with the string passed to the method; otherwise, they return

False.

• These methods can also be used to compare strings. In case

the string passed as argument to the method is equivalent to

the string object. They will return True.

• See following example.

Example: startswith() and endswith()

The split() String Method

• This method is very helpful in editing string sentences.

Since strings are immutable data types, the split()

method returns a list data type which is mutable and

could be edited.

• The split() method is the opposite of a join() method

(shown later). It is called on a single string and returns

a list containing the string components.

• By default, split() breaks down the strings using white

spaces. This behaviour can be changed or customised.

Example: split() String Method

• You can pass a delimiter to the split() method to

specify a different string to split upon. See following

example.

split() String Method

• A common usage of split() is to split multiline strings along

the newline characters.

The join() String Method

• The join() method is useful when you have a list of strings

that need to be joined together into a single string value.

• The join() method can be:

• called on a string,

• get passed a list of strings as arguments,

• and returns a string.

• The returned string is a concatenation of each string in the

passed-in argument list.

• See following example:

Example: join() String Method

• Notice that the string join() is called on, is inserted between each

string of the list argument.

• Remember that join() is called on a string value and is passed a string

iterable data type (string, list, tuple, dictionary) and not the other way

round.

Justifying Text with rjust(), ljust()

Method

• The rjust() and ljust() string methods return a padded version

of the string they are called on, with spaces inserted to justify

the text.

• The first argument to both methods is an integer specifying the

length for the justified string. Note that the length of the string

called on is included in this value. See following examples.

Justifying Text with rjust(), ljust()

Method

• An optional second argument to rjust() and ljust() will

specify a fill character other than a space character.

• Example:

Justifying with center() Method

• The center() string method works like ljust() and rjust() but

centres the text rather than justifying it to the left or right.

• Example:

• These methods are especially useful when you want to

print tabular data to have the correct spacing.

Sample Justifying Usage Scenario

• Formatting and printing picnic items in tabular form.

Sample Usage Scenario: Output

Copying and Pasting Strings with the

pyperclip Module

• The pyperclip module has copy() and paste() functions that can send

text to and receive text from your computer’s clipboard.

• Sending the output of your program to the clipboard will make it easy,

for example, to paste it on an email, word processor or some other

software.

• This module is a third-party module and requires to be installed

before usage.

• From OS X Terminal, issue command “python3 -m pip3 install pyperclip”

• From Linux Terminal, issue “sudo apt-get install python3-pip”

• You may need additional installations to get it working in Linux.

• From Window command line interface, issue “py –m pip install pyperclip”

Example: pyperclip Module

• If something outside your program changes the

clipboard content, the paste() function will return it.

• For example: (Just copied the above text to clipboard)

Pyperclip Usage Scenario: Password

locker

• You probably have accounts on many different websites.

It’s a bad habit to use the same password for each of them

because if any of those sites has a security breach, the

hacker will learn the password to all of your other

accounts.

• It’s best to use password manager software on your

computer that uses one master password to unlock the

password manager. In this scenario, we want to create a

password manager (though not secure, does not have a

master password) that can help you manage password for

different websites.

Step 1: Program Design and Data

Structures

• A user want to be able to run this program with a command

line argument that is the account’s name – for instance, so

that the corresponding password will be copied to the

clipboard.

• The user can then paste the content of the clipboard into

the password field to authenticate herself.

• This way, the user can have long, complicated passwords

without having to memorise them.

• Since we want to associate each accounts name with its

password, we can use dictionary to organise these data.

Password Locker: Data Structure

Step 2: Handle Command Line

Arguments

• The command line arguments will be stored in the array

variable sys.argv.

• The following describes the content of the sys.argv array:

• First item is a string representing the program name (pw.py)

• Second item is the first command line argument – the name of

the particular account in our use case.

• And so on.

• Since the command line argument is mandatory, you

should display a usage message to the user if they forgot to

provide it.

Password Locker: Command Line Argument

Step 3: Copy the Right Password

• Now that the account name is stored as a string in a variable

account, you need to see whether it exists in the password

dictionary as a key.

• If so, you want to copy the key’s value to the clipboard using

pyperclip.copy() function. (We need to import the pyperclip

module first)

• Note that you do not actually need the account variable, you

could just use sys.argv[1] everywhere account is used in the

program.

• But the account variable name is much more readable than

something cryptic like sys.argv[1].

Password Locker: Full Solution

Password Locker: Invocation

• The program is designed to be called from the

command line.

• Example invocation:

• python3 pw.py email

• In the above invocation “email” represents the

account name. With this invocation, the password

associated with the specified email account is copied

to the clipboard and you can simply paste in the

password field.

Thank You!