These are the slides of the first event of the meetup group Learn Python Den Haag. It covers some aspects of the basics of Python programming.

1. Introduction to the basics of
Python programming
(PART 1)
by Pedro Rodrigues (pedro@startacareerwithpython.com)

2. A little about me
 Name: Pedro Rodrigues
 Origin: Luanda (Angola)
 In the Netherlands since 2013
 Former CTO and Senior Backend Engineer
 Freelance Software Engineer
 Book author: Start a Career with Python
 Coach

3. Why this Meetup Group?
 Promote the usage of Python
 Gather people from different industries and backgrounds
 Teach and Learn

4. What will be covered
 First steps with the interactive shell: CPython
 Variables and Data types
 Single and Multi variable assignment
 Immutable: strings, tuples, bytes, frozensets
 Mutable: lists, bytearrays, sets, dictionaries
 Control Flow
 if statement
 for statement
 Range, Iterable and Iterators
 while statement
 break and continue

5. What is Python?
 Dutch product: create by Guido van Rossum in the late 80s
 Interpreted language
 Multi-paradigm: Procedural (imperative), Object Oriented, Functional
 Dynamically Typed

6. Python interpreter
 CPython: reference, written in C
 PyPy, Jython, IronPython
 help()
 dir()

7. Hello, world!

8. Variables
 Binding between a name and an object
 Single variable assignment: x = 1
 Multi variable assignment: x, y = 1, 2
 Swap values: x, y = y, x

9. Data Types
 Numbers: int (Integers), float (Real Numbers), bool (Boolean, a subset of int)
 Immutable Types: str (string), tuple, bytes, frozenset
 Mutable Types: list, set, bytearray, dict (dictionary)
 Sequence Types: str, tuple, bytes, bytearray, list
 Determining the type of an object: type()

10. Numbers: int and float
 1 + 2 (addition)
 1 – 2 (subtraction)
 1 * 2 (multiplication)
 1 / 2 (division)
 1 // 2 (integer or floor division)
 3 % 2 (modulus or remainder of the division)
 2**2 (power)

11. Numbers: bool (continuation)
 1 > 2
 1 < 2
 1 == 2
 Boolean operations: and, or, not
 Objects can also be tested for their truth value. The following values are false:
None, False, zero of any numeric type, empty sequences, empty mapping

12. str (String)
 x = “This is a string”
 x = ‘This is also a string’
 x = “””So is this one”””
 x = ‘’’And this one as well’’’
 x = “””
This is a string that spans more
than one line. This can also be used
for comments.
“””

13. str (continuation)
 Indexing elements: x[0] is the first element, x[1] is the second, and so on
 Slicing:
 [start:end:step]
 [start:] # end is the length of the sequence, step assumed to be 1
 [:end] # start is the beginning of the sequence, step assumed to be 1
 [::step] # start is the beginning of the sequence, end is the length
 [start::step]
 [:end:step]
 These operations are common for all sequence types

14. str (continuation)
 Some common string methods:
 join (concatenates the strings from an iterable using the string as glue)
 format (returns a formatted version of the string)
 strip (returns a copy of the string without leading and trailing whitespace)
 Use help(str.<command>) in the interactive shell and dir(str)

15. Control Flow (pt. 1): if statement
 Compound statement
if <expression>:
suite
elif <expression2>:
suite
else:
suite

16. Control Flow (pt. 2): if statement
age = int(input(“> “))
if age >= 30:
print(“You are 30 or above”)
elif 20 < age < 30:
print(“You are in your twenties”)
else:
print(“You are less than 20”)

17. list
 x = [] # empty list
 x = [1, 2, 3] # list with 3 elements
 x = list(“Hello”)
 x.append(“something”) # append object to the end of the list
 x.insert(2, “something”) # append object before index 2

18. dict (Dictionaries)
 Mapping between keys and values
 Values can be of whatever type
 Keys must be hashable
 x = {} # empty dictionary
 x = {“Name”: “John”, “Age”: 23}
 x.keys()
 x.values()
 x.items()

19. Control Flow: for loop
 Also compound statement
 Iterates over the elements of an iterable object
for <target> in <expression>:
suite
else:
suite

20. Control Flow: for loop (continuation)
colors = [“red”, “green”, “blue”, “orange”]
for color in colors:
print(color)
colors = [[1, “red”], [2, “green”], [3, “blue”], [4, “orange”]]
for i, color in colors:
print(i, “ ---> “, color)

21. Control Flow: for loop (continuation)
 Iterable is a container object able to return its elements one at a time
 Iterables use iterators to return their elements one at a time
 Iterator is an object that represents a stream of data
 Must implement two methods: __iter__ and __next__ (Iterator protocol)
 Raises StopIteration when elements are exhausted
 Lazy evaluation

22. Challenge
 Rewrite the following code using enumerate and the following list of colors:
[“red”, “green”, “blue”, “orange”] .
(hint: help(enumerate))
colors = [[1, “red”], [2, “green”], [3, “blue”], [4, “orange”]]
for i, color in colors:
print(i, “ ---> “, color)

23. Control Flow: for loop (continuation)
 range: represents a sequence of integers
 range(stop)
 range(start, stop)
 range(start, stop, step)

24. Control Flow: for loop (continuation)
colors = [“red”, “green”, “orange”, “blue”]
for color in colors:
print(color)
else:
print(“Done!”)

25. Control Flow: while loop
 Executes the suite of statements as long as the expression evaluates to True
while <expression>:
suite
else:
suite

26. Control Flow: while loop (continuation)
counter = 5
while counter > 0:
print(counter)
counter = counter - 1
counter = 5
while counter > 0:
print(counter)
counter = counter – 1
else:
print(“Done!”)

27. Challenge
 Rewrite the following code using a for loop and range:
counter = 5
while counter > 0:
print(counter)
counter = counter - 1

28. Control Flow: break and continue
 Can only occur nested in a for or while loop
 Change the normal flow of execution of a loop:
 break stops the loop
 continue skips to the next iteration
for i in range(10):
if i % 2 == 0:
continue
else:
print(i)

29. Control Flow: break and (continue)
colors = [“red”, “green”, “blue”, “purple”, “orange”]
for color in colors:
if len(color) > 5:
break
else:
print(color)

30. Challenge
 Rewrite the following code without the if statement (hint: use the step in range)
for i in range(10):
if i % 2 == 0:
continue
else:
print(i)

31. Reading material
 Data Model (Python Language Reference):
https://docs.python.org/3/reference/datamodel.html
 The if statement (Python Language Reference):
https://docs.python.org/3/reference/compound_stmts.html#the-if-statement
 The for statement (Python Language Reference):
https://docs.python.org/3/reference/compound_stmts.html#the-for-statement
 The while statement (Python Language Reference):
https://docs.python.org/3/reference/compound_stmts.html#the-while-statement

32. More resources
 Python Tutorial: https://docs.python.org/3/tutorial/index.html
 Python Language Reference: https://docs.python.org/3/reference/index.html
 Slack channel: https://startcareerpython.slack.com/
 Start a Career with Python newsletter: https://www.startacareerwithpython.com/
 Book 15% off (NZ6SZFBL): https://www.createspace.com/6506874

33. set
 Unordered mutable collection of elements
 Doesn’t allow duplicate elements
 Elements must be hashable
 Useful to test membership
 x = set() # empty set
 x = {1, 2, 3} # set with 3 integers
 2 in x # membership test

34. tuple
 x = 1,
 x = (1,)
 x = 1, 2, 3
 x = (1, 2, 3)
 x = (1, “Hello, world!”)
 You can also slice tuples

35. bytes
 Immutable sequence of bytes
 Each element is an ASCII character
 Integers greater than 127 must be properly escaped
 x = b”This is a bytes object”
 x = b’This is also a bytes object’
 x = b”””So is this”””
 x = b’’’or even this’’’

36. bytearray
 Mutable counterpart of bytes
 x = bytearray()
 x = bytearray(10)
 x = bytearray(b”Hello, world!”)