Strings (add, f-strings, length, replace, UPPER, lower, trim/strip, padding, escape sequences)

Musical Intro

Introduction

In programming, a “string” is simply text data – like words in a book or letters in your name.
Technically it is a variable, where you store text in it.

# when we have a text string
aTextString = "hello world"

# then we can print it to show it's content
print(aTextString)

Now you need to make a choice, how you want to learn it:

1. You can use AI to teach you. Then you can learn, by your own exploration and in any programming language (scroll down to Using AI)
2. You can use the result I got, from using AI. Then you can rely on my experience to filter it.(keep on reading)
3. You can also do both in any order :-)

Joining Strings Together (Adding / Concatenation)

# given we have two texts
var1 = "hello"
var2 = "world"

# when we add them together
result = var1 + var2 

# then they put together
print(result)
assert result == "helloworld"

Adding works differently with numbers:

# given we have two numbers
var1 = 1
var2 = 2

# when we add them together
result = var1 + var2 

# then they give the sum
print(result)
assert result == 3

If we put the numbers as text (with quotation marks), then they will add as strings and not numbers:

# given we have two numbers
var1 = "1"
var2 = "2"

# when we add them together
result = var1 + var2 

# then they put together (and not the sum)
print(result)
assert result == "12"

Also if you want to have a space between to words, that you add together, then you need to remember to also add a space:

# given we have two texts
text1 = "hello"
text2 = "world"
space = " " # the space

# when we add them together
result = text1+ space + text2

# then they put together
print(result)
assert result == "hello world"

Challenge, weather report

Try to write a code, where you

# given the weather is describe with the following parts:
city = "Praestoe"
temperature = "22°C"

# When we concatenate them to form a weather report
# (write your code here)

# Then the result should exactly match the expected report.
print(result)
assert result == "The current weather in Praestoe is 22°C"

result = "The current weather in " + city + " is " + temperature

G-, F-, Template- and interpolated-strings

G-Strings are a special kind of strings that are used in Groovy. They have other names in other languages:

They seem much more complex that a regular string, except they make our lives much easier.

Which one of these text addition do you find easiest to use?

# example 1 (the regular string)
result = "Mr. "+ name

# example 2 (the f-string)
result = f"Mr. {name}"

When we write a f in front of a “
Then we can just add { } with a variable name inside the text.

This makes it much easier with much more complicated strings, where we can use spaces inside the string, instead of adding extra spaces or adding them as variables:

# example 1 (the regular string)
result = title + " " + firstName + " " + lastName

# example 2 (the regular string with space variables)
result = title + space + firstName + space + lastName

# example 3 (the f-string)
result = f"{title} {firstName} {lastName}"

Challenge, F-weather

Rewrite the previous challenge by using f-strings

# given the weather is describe with the following parts:
city = "Praestoe"
temperature = "22°C"

# When we concatenate them to form a weather report
# (write your code here)

# Then the result should exactly match the expected report.
print(result)
assert result == "The current weather in Praestoe is 22°C"

Slicing

Since we can add strings together, then we can also slice them up into smaller parts and only keep the important part.

# given we have a text string
greeting = "Hello world"

# when we slice off the first letter
without_first = greeting[1:]

# then we only have the rest left
print(without_first)
assert without_first == "ello world"

And the same can be done on the other side of the string:

# given we have a text string
greeting = "Hello world"

# when we slice of the 2 last letters
without_last = greeting[:-2]

# then we only have the rest left
print(without_first)
assert without_first == "hello wor"

We use negative numbers, to count letters from the back of the string
We use positive numbers, to count letters from the front of the string

Challenge, slicing the world

# given we have a text string
greeting = "12345"

# when the ? is replaced with a positive number
result_1_1 = greeting[?:]
result_1_2 = greeting[:?]
result_1_3 = greeting[?:?]

# and the ? is replaced with a negative number
result_2_1 = greeting[:-?]
result_2_2 = greeting[-?:]
result_2_3 = greeting[-?:-?]

# then the strings are sliced to
assert result_1_1 == "2345"
assert result_1_2 == "12"
assert result_1_3 == "2"

assert result_2_1== "1234"
assert result_2_2== "45"
assert result_2_3== "4"

result_1_1 = greeting[?:] # [1:] from after letter 1
result_1_2 = greeting[:?] # [:2] until after letter 2
result_1_3 = greeting[?:?] # [1:2] from after letter 1 until after letter 2

result_2_1 = greeting[:?] # [:-1] until before letter 1 from behind
result_2_2 = greeting[?:] # [-2:] from before letter 2 from behind
result_2_3 = greeting[?:?] # [-2:-1] from before letter 2 from behind until

result_3_1 = greeting[?:?] # [1:-2]from after letter 1 until before letter -2 from behind
result_3_1 = greeting[?:?] # [-3:1]from after letter 1 until before letter -2 from behind

Length of a string

We can also measure the length of a string, which can be important if we want a password to have a minimum length.

Trim or strip

Sometimes Strings are written with spaces before and after the text: ” hello world “

The easiest way to remove the spaces is to use the command strip() in Python, trim() in JavaScript and Groovy, and Trim() in C#.

# Given the original text with leading and trailing space
originalText = " hello world "
print(f"original: ${originalText }")

# When we apply strip in it's 3 variations:
text1 = originalText.lstrip()
text2 = originalText.rstrip()
text3 = originalText.strip()

# Then text1 should be with no leading whitespace
print(f"lstrip:  |{text1}|")
assert text1 == "hello world "

# And text2 should be with no trailing whitespace
print(f"rstrip:  |{text2}|")
assert text2 == " hello world"

# And text3 should be with no leading or trailing whitespace
print(f"strip:   |{text3}|")
assert text3 == "hello world"

Padding

To add spaces, or any other symbol, before a text can be done with rjust() in Python, padStart() in JavaScript, padLeft() in Groovy, PadLeft() in C#.

To add spaces, or any other symbol, after a text can be done with ljust() in Python, padEn() in JavaScript, padRight() in Groovy, PadRight() in C#.

# Given product names and prices
product1 = "Orange"
price1 = "25 EUR"

product2 = "Computer"
price2 = "1000 EUR"


# When combining product names and prices with normal addition
productText1a = product1 + " " + price1
productText2a = product2 + " " + price2

# Then the product text is not formatting in a pretty way
print(productText1a)
print(productText2a)
print("---------  ---------")


# When aligning product names with spaces as padding
productText1b = product1.ljust(10, " ") + price1.rjust(10, " ")
productText2b = product2.ljust(10, " ") + price2.rjust(10, " ")

# Then the product text should have a pretty formatting
print(productText1b)
print(productText2b)
print("---------  ---------")


# When aligning product names with dots as padding
productText1c = product1.ljust(10, ".") + price1.rjust(10, ".")
productText2c = product2.ljust(10, ".") + price2.rjust(10, ".")

# Then the product text should have even prettier formatting
print(productText1c)
print(productText2c)
print("---------  ---------")

Which will give the following output:

Escape sequences to make line breaks, tabulators, and quotes within quotes

To have a line break in a string, then a \n can be put into it. Because we can’t write:

print("line 1
line 2")
# creates an error

To have a tab a \t can be use, even though we sometimes can add tabs, but not always. Sometimes they are added as 2 or 4 spaces instead of a tab:

print("word 1  word 2")
# creates an error

To have a quote within a quote requires an \”, because we can’t write the following without creating an error:

print("word 1 "word 2" word 3")
# creates an error

And because we use \ to write special characters, we need to write \\ to tell the computer we want to write an \, otherwise it will expect an special character.

To write it correctly please do:

Conclusion

Today, we took a fun dive into the colorful world of strings, discovering that strings are like little containers for text—holding everything from single words to lengthy paragraphs.

We kicked things off by learning how to add strings together, transforming “hello” and “world” into “hello world.”

We then looked into f-strings (Python), G-strings (Groovy), template-strings (JavaScript) and interpolated strings (C#).

We also got crafty with slicing strings, which is a bit like sculpting: you chisel away the parts you don’t need or shuffle them around to create something entirely new.

And we played around with replacing a word in a string with another word. Quite fancy when you want to anonymize a text.

We also looked into the length of strings. It’s like having a tiny ruler at your fingertips, perfect for checking the length of a text, ensuring passwords meet security standards, or just satisfying your curiosity about how much you’ve actually typed.

We played with to uppercase and lowercase, which helps keep everything looking neat and tidy, no matter how chaotic the input might be.

We ended with a fun exercise where we had to combine all what we learned together, by making “eLISAbeTH “into “Elisabeth”

We looked into trim/strip to remove spaces.

Padding to add spaces and other symbols.

Escape sequences such as line breaks, tabulators, and quotes within quotes.

By now, you should feel pretty equipped to handle text in your programming projects. Whether you’re crafting messages, tidying up data, or just indulging your inner nerd, the skills you’ve embraced today are essential tools in your programming kit. Let’s keep that inner child curious and eager to learn more as we continue exploring the vast and vibrant world of coding!

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Using AI

All this have been created with the cooperation with AI.

Often it can be more useful just to learn, what is needed in the moment, than to learn everything about a topic. This is where AI is perfect.

We can use the free ChatGPT 3.5 to learn about operators. You are welcome to try other and if you do, please write a comment!

Essential prompts can be:

Learning about Strings

I would like to learn about Strings (text) in Python.
What things are critical to learn?

When we want to learn more about the topic

I would like to learn more about Escape Sequences, what should I be able to do?

It answered much more, but there is no need to show it all, because the amount of data can be overwhelming: (Multiline Strings, Unicode Character, Escape Sequence as Literal, Control Characters, Hexadecimal and Octal Escapes)

Take one of them and go further into it.

Then you can explore each theme with:

I would like to learn more about Special Characters such as '\n', '\t', and '\\'.

Can you show me:
1. an example of how it works? (in python)
2. a real world application of it? (in python)

I want the code examples to be written with given, when, and then steps.
The then step needs to contain a print and assert (for manual and automatic verification)

And we can always test the code in our web editors: 💻 Python / 💻 JavaScript / 💻 Groovy / 💻 C#

To get an assignment to learn from:

Can you make a assignment for me to solve?
It has to be about using Special Characters such as '\n', '\t', and '\\'.

The assignment needs to be written in Python as comments.
Use only given, when, and then comments. No code.

And sometimes you might need to start a new session.

Sometimes the AI makes a mistake like writing Given, Then, When (wrong order) and sometimes starting a new session makes it go away.

And you can get AI to solve it for you:

Can you please solve this assignment for me in Python code?
--
# Given a string containing multiple lines of text separated by '\n' characters,
# where some words are separated by '\t' characters,
# and some backslashes are used to escape special characters.

# When the string is given as input,
# Then write a Python program to perform the following tasks:

# 1. Split the string into individual lines using the '\n' character as the delimiter.
# 2. For each line, split the line into words using the '\t' character as the delimiter.
# 3. If a word contains the sequence '\\', replace it with a single backslash character '\'.
# 4. Print each word on a new line.

# For example:
# Given input string:
# "Hello\tworld!\nThis\tis\tan\texample\nString\twith\\tSpecial\tCharacters\n"

# The output should be:
# Hello
# world!
# This
# is
# an
# example
# String
# with\tSpecial
# Characters
--

And we can run it in our web editor:

You can ask for a new assignment – as many times as you want.

You can make the AI solve it for you.
You can make the AI help you solve it.
You can solve it yourself.
Limitless learning with a 24/7 tutor!!!

Congratulations – Lesson complete!