Next pages: Python editor // Collections // Conditions // Loops // Working with text files // Exercises
Inspiration: https://github.com/mikekestemont/ghent1516
Python documentation: https://docs.python.org/3/
Variables & Strings
- Introduction to the objects string & list with their different attributes
- Using the shell
A string is a chain of characters / text and can contain any type of characters.
A string is defined by ” “
Write text using string
>>> print("La Cambre")
Exercise: Write your name
Add text
>>> print("Brussels"+"Paris")
>>> print("Brussels "+"Paris")
Exercise: Write your address
Composing a sentence
>>> print("Paris", "to", "London", "via", "Brussels")
>>> print("Paris to London via Brussels")
Exercise: Write your favourite expression
Multiply
>>> print(3*3)
>>> print(3 * "algolit" + " in Brussels")
Exercise: Write 'I write the alphabet' 3 times.
Note: there are always different possible solutions.
Changing from Python in the shell to the editor: https://www.anaisberck.be/python-editor/
Write a string as a variable
This avoids having to retype your string each time you use it You can change values at any time of the writing process.
letter = "a"
print(letter)
word = "Python"
print(word)
sentence = "I learn to read and write again in Python."
print(sentence, letter)
Exercise: Print your letter, word, sentence
Add punctuation
print(letter + " " + word + " " + sentence + ".")
print(letter + "! " + word + "? " + sentence + ".")
letter = "i"
print letter + "! " + word + "? " + sentence + "."
Exercise: change content of one of variables, over and over.
See how result changes
Calculate!
Calculate the length of a string
print(len(letter))
print(len(word))
print(len(sentence))
print(len(word))+2)
And more
a_number = len(word)+2
print(a_number)
a_number += 3
print(a_number)
Exercise: Compose a sentence word by word,
specifying each word as a variable.
The length of the sentence is 20.
Letters/words/sentences as fields or grids
Each letter occupies a specific position. We can access strings using indexes.
Note: computer starts to count from 0
print(word[0])
print(word[3])
Exercise: What is the middle letter of your sentence?
Slicing and concatenating strings
in order to select letters & compose new words
- Find last letter
print(word[-1])
- Find last but one letter
print(word[-2])
- Find first two letters
print(word[0:2])
or
print(word[:2])
- Find 3 letters in the middle
print(word[2:5])
- Find from 3rd letter till end
print(word[2:])
Exercise: If the word is "solidarity", what do you read here?
word[:5] + word[3:]
Exercise: rewrite the word as 'liquidity', using slicing
replace()
The
replace()
function is another function which can be called on a string. It will replace all occurrences of a specified substring with another string.
text = "Joe Biden won the elections." text = text.replace(" the elections", "") print(text) text = text.replace("Joe Biden", "Donald Trump") print(text)
Exercise:
text = "Research shows that it is possible to understand text when all vowels are removed"
Change case
lower()
converts a string to lowercase characters and upper()
returns an uppercased version.
print(letter.lower())
print(sentence.upper())
Write first word of sentence with capital letter”
print(sentence.capitalize())
Note the difference
print(sentence.title())
print(word.title())
What you’ve learned
- variable
- value
- assignment operator (=)
- difference between variables and values
- integers (numbers)
- print()
- len()
- slicing and concatenating
- replace()
- lower()
- upper()
- capitalize()
- title()