Python for beginners

Literary Python for Beginners

• • run python 2.7 – installed by default on all platforms (Ubuntu, Mac, Windows)

$ python

>>>

• • install python idle 2.7 – ways to interact with Python: shell + editor

LETTER * WORD * SENTENCE

• Introduction to the objects string & list with their different attributes
• uses the shell or integrated development environment

# USING STRINGS

A string is a chain of characters / text and can contain any type of characters

A string is defined by " "

* write letter using STRING

>>> "a"

* write several letters

>>> "a, b, c, d"

* write combinations

>>> "a" + "b"

>>> 3

>>> "a" + "and" + "b"

>>> "a" + " and " + "b"

>>> "a" + "+ " + 3 + " is a3" ***

>>> 3*3

>>> "a" + "+ " + "3" + " is a3"

>>> 3 * "algolit" + " in wtc25"

• • Exercise: Write 'I write the alphabet 3 times.'

Note: there are always different possible solutions

* write string as variable

• • 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 = "algolit"

>>> print word

>>> sentence = "I learn to read and write again at wtc25"

>>> 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!

• • the length of the string

>>> len(letter) >>> len(word) >>> len(sentence)

• • we can also consider the letter/word/sentence as fields or grids, in which each letter occupies a specific position

Note: computer starts to count from 0

>>> word[0] >>> 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

>>> zin[-1]

• • find last but one letter

>>> word[-2]

• • find first two letters

>>> word[0:2]

or

>>> word[:2]

• • find 3 letters in the middle

>>> word[2:5]

• • find from 3rd letter till end

>>> word[2:]

• • Exercise: If the word is "solidarity" is, what do you read here?

word[:5] + word[3:]

• • Exercise: rewrite the word as 'liquidity', using slicing

* write with capitals

>>> print letter.lower()

>>> print sentence.upper()

* write first word of sentence with capital letter

>>> print sentence.capitalize()

* note the difference

>>> sentence.title()

>>> word.title()

From STRINGS to LISTS

• LISTS are MUTABLE vs immutable STRINGS

That is the reason you want to change your string into a list:

>>> sentence.split()

and save it as a new variable:

>>> list_words = sentence.split()

* some of the attributes of string can be used for lists

• • Exercise: which previously mentioned attributes function for lists?

* replace a word in a list

>>> list_words[3] = "wtc25"

>>> print list_words

* remove words

>>> list_words[2:3] = []

Note: list_words[2] = [] → this removes your 3rd element and replaces it by an empty sublist ('nested list')

* put back words

>>> list_words[2:3] = ["so", "exciting"]

* shorten a list

>>> list_words[-3:]

• and save the shortened list into a new variable – the old continues to exist

>>> yezzzz = list_words[-3:]

* combine lists, group two in one

>>> text = [list_words, yezzzz]

* call an element of a sublist

>>> word = text[1][2]

* concatenate lists, merge two into one

>>> print(list_words + yezzzz)

>>> poem = list_words + yezzzz

*add words to your list

>>> poem.append("is") >>> print(poem)

* sort your list alphabetically

>>> poem.sort()

* transform your list into a string again

>>> " ".join(poem)

NOTE: the whitespace / try without

>>> " ".join(poem) + "?"

• empty your list // you have a brand new sheet of paper :-)

>>> poem[:] = []