CoderDojo: Intermediate Python programming course

https://github.com/alaudo/coderdojo-pythonhttp://enigmacode.azurewebsites.net/
Python programming
intermediate course
Created by Alexander Galkin aka Alaudo
published under Creative Common License

Course outline
• Session 1: Leveling the ground (basic Python)
• Session 2: Strings and collections
• Session 3: Functions, Dictionaries etc..

CONTROL FLOW AND VARS
Session 1

Control flow
print(“hello”)
print(“My name is Alex”)
print(“I am your new master”)
print(“This is command #4”)

Variables
• Variables are basically boxes that you can put
stuff in
• They store the values you assign them

Variables
print("Hello, I am python, your servant")
master = input("What is your name, master? ")
print("I am glad to welcome you")
print(master)
print("my master")

Types
• A type is the kind of value that a value (and
variable) can be
• There are numerous kinds of types
• String, Integer, Boolean are examples

Types
word = "Word"
print(type(word))
number = 3
print(type(number))
fraction = 2/7
print(type(fraction))
print(fraction)
equation = 4 > 8
print(type(equation))
print(equation)

Boolean Operators
• These are logic checks that you can use to
determine when actions should happen
• and, or, != (not equal), == (equal to),
> (greater than), < (less than), >= (greater than
or equal to), <= (less than or equal to), and
True/False

Important
• In computers the equal sign can mean
different things!!!
• In Python
=  assignment (let var a take the value b)
==  comparison (if var a equals var b)

variable1 = 1
variable2 = 5
variable3 = 5
variable1 == variable2
variable1 != variable2
variable1 < variable2
variable1 > variable2
variable1 <= variable2
variable2 >= variable3
variable1 < variable2 and
variable1 < variable2 or
False
True
True
False
True
True
False
True

What can we compare?
• Numbers ( 2, 3, 5, 5.5, 7.5, 8 )
• Strings (“alex”, “bert”, “cindy”)
• Dates and times
(for all orderable types – two values)
• Numbers and strings?
• Numbers and dates/times?

If/Else Statement
• A statement that will run one set of code if a
condition is met, and the other set of code if a
condition is not met.
• Condition is written as a Boolean expression
that returns True or False

If/Else
person1 = input("What is the first name? ")
person2 = input("What is the second name? ")
if person1 > person2:
print(person1)
print("has won")
else:
print(person2)
print("has won")

Elif
• You can chain if/else statements together with
elif
• This allows you to check for multiple
conditions

If/Else/Elif
print(person1)
print("has won")
elif person1 == person2:
print("friendship")
print("has won")
else:
print(person2)
print("has won")

While Loops
• Loop while a condition is met
• Runs the code inside of them every time you
iterate

while
answer = input("Do you want to play a game? ")
while answer == "yes":
print(person1)
print("has won")
print("friendship")
print("has won")
else:
print(person2)
print("has won")

For Loops
• Loop over a given range/set/list
• Run the code inside of them every time you
iterate

for in range
answer = int(input("How many times do you want to play? "))
for i in range(0,answer):
print(person1)
print("has won")
print("friendship")
print("has won")
else:
print(person2)
print("has won")

STRINGS AND COLLECTIONS
Session 2
https://github.com/alaudo/coderdojo-python
http://enigmacode.azurewebsites.net/

Recap from last session
age = input("What is your age? ")
if age =< 10:
print("You are below 10!")
if age = 10:
print("You are exactly 10!")
if age => 10:
print("Your are above 10!")
How many errors can you find here?

Recap from last session
m = 3
s = 0
for i in range (1,m):
s = s + i
print(s)
What number will this program print?

while
while answer == "yes":
print(person1)
print("has won")
print("friendship")
print("has won")
else:
print(person2)
print("has won")
How to remove the duplicate line?

Advanced loops
• break
• continue
• pass
while True:
if (answer != "yes"):
break
else:
print(person1)
print("friendship")
else:
print(person2)
print("has won")

Strings: what do we now?

Strings: what do we now and what
don’t?
• Get with “input”
command
• Compare as numbers
• Compare with “==“ and
“!=“
• Print with “print”
command

Strings: what should we know?
• Get with “input”
command
• Compare as numbers
• Compare with “==“ and
“!=“
• Print with “print”
command
• How to check if string is
empty?
• How to get string length?
• How to get a part of a
string?
• How to replace one
symbol with another?
• How to reverse string?
• How to split string?
• How to stich many strings
together?

Strings & math
• What happens if we:
o string1 + string2
o string1 – string2
o string1 * 10
o string2 / 5
o string3 % 5
• How can we:
stitch strings
remove part of string
copy string
format string

How to test for empty string?
text = input("Enter something ")
if (text):
print("This text is not empty")
else:
print("This text is EMPTY")
What about just spaces in the string?

How find how long a string is?
text = input("Enter something ")
print (len(text))
But how to print the text WITH numbers?

Pretty printing in Python?
print("My length is " + str(len("My length is")))
print("My favorite programming language is %s " % "python")
print("{} and {} are best friends".format("me", "my papa"))
print("My name is {name} and I am {age} years old".format(name = "Alex", age = 37))

Pretty printing in Python?
print("I am a good programmer".replace("good","not really good"))
print("<***>".join(["one","two","three","four"]))
print(''.join(reversed("I am a good string")))
print("I am a good athlete".split(" "))

Lists
• A list is a container that holds other
objects/values
• A list can be as large as you need it to be
• You can access the values inside a list at any
time as long as you have the list

Hidden lists
for i in range(0,10):
print(i)
print(list(range(0,10)))
txt = "pizza is no longer hot"
for i in txt:
print(i)
print(list(txt))
Lists, they are everywhere… 

Browsing lists
a = "Jingle bells, Jingle bells
Jingle all the way Oh what fun it
is to ride"
print(a[0])
print(a[1])
print(a[0:10])
print(a[0:10:2])
print(a[::3])
print(a[::-1])

Browsing lists (2)
a = "Jingle bells, Jingle bells
Jingle all the way Oh what fun it
is to ride“
a = a.split(“ “)
print(a[0])
print(a[1])
print(a[0:10])
print(a[0:10:2])
print(a[::3])
print(a[::-1])

CoderDojo: Intermediate Python programming course

ASCII manipulations
a = "Jingle bells, Jingle bells Jingle all the way
Oh what fun it is to ride"
l = []
for i in a:
l.append(ord(i))
print(l)
m = []
for t in l:
m.append(t + 2)
print(m)
v = []
for k in m:
v.append(chr(k))
print(''.join(v))

List comprehensions
a = "Jingle bells, Jingle bells Jingle all the way
Oh what fun it is to ride"
l = [ord(i) for i in a]
print(l)
m = [t + 2 for t in l]
print(m)
v = [chr(k) for k in m]
print(''.join(v))

Challenge begins!! 
https://github.com/alaudo/coderdojo-python
http://enigmacode.azurewebsites.net/

FUNCTIONS, DICTIONARIES ETC
Session 3

Trying to decode…
PPhhoottoonnss hhaavvee nneeiitthheerr mmoorraallss nnoorr
vviissaass..
How can we decode this?

Trying to decode…
vviissaass..
text = "PPhhoottoonnss hhaavvee nneeiitthheerr mmoorraallss nnoorr vviissaass.."
print(text[::2])

Trying to decode…
What about this?
IIIInnnnssssiiiiddddeeee eeeevvvveeeerrrryyyy ssssmmmmaaaalll
lllll pppprrrroooobbbblllleeeemmmm iiiissss aaaa bbbbiiiigggg
oooonnnneeee ttttrrrryyyyiiiinnnngggg ttttoooo ggggeeeetttt
ggggoooovvvveeeerrrrnnnnmmmmeeeennnntttt ffffuuuunnnnddd
diiiinnnngggg....

Trying to decode…
How can we skip the burden of writing the same code again and again?
IIIInnnnssssiiiiddddeeee eeeevvvveeeerrrryyyy ssssmmmmaaaalll
lllll pppprrrroooobbbblllleeeemmmm iiiissss aaaa bbbbiiiigggg
oooonnnneeee ttttrrrryyyyiiiinnnngggg ttttoooo ggggeeeetttt
ggggoooovvvveeeerrrrnnnnmmmmeeeennnntttt ffffuuuunnnnddd
diiiinnnngggg....
text =
"IIIInnnnssssiiiiddddeeee eeeevvvveeeerrrryyyy ssssmmmmaaaallllllll pppprrrroooobbbbl
llleeeemmmm"
print(text[::4])

Functions
• Functions are like tools: you can re-use the same tool
in many situations to solve similar problems
• Functions take input – something they are applied to
– and return the result back
• In addition to input the functions can also take any
number of parameters to specify what and how the
function should be applied

Functions as reusable components
vviissaass..
We parameterize functions instead of re-writing code
def dedouble(text, count):
return text[::count]
print(dedouble(“PPhhoottoonnss hhaavvee”,2))
print(dedouble(“IIIInnnnssssiiiiddddeeee”,4))

Further decoding
.ti esu ot tnaw lliw toidi na ylno dna esu nac
toidi na metsys a ngiseD
What about this?

Further decoding
.ti esu ot tnaw lliw toidi na ylno dna esu nac
toidi na metsys a ngiseD
def palindrome(text):
return text[::-1]

More advanced
it. invent is do can we All all. at future the predict really can't We
What about this?

More advanced
it. invent is do can we All all. at future the predict really can't We
Well done!!
def yoda(text):
return " ".join(text.split(" ")[::-1])

Further and further
s'tI suoregnad ot eb thgir nehw eht tnemnrevog si .gnorw
What about this?

List: recap
1. How to create an
empty List?
2. How to add element to
a list?
3. How to test if element
is in the list?

List: recap
1. How to create an
empty List?
2. How to add element to
a list?
3. How to test if element
is in the list?
1. lst = []
2. lst.append(elem)
3. if elem2 in lst:

Further and further
s'tI suoregnad ot eb thgir nehw eht tnemnrevog si .gnorw
def mirror(text):
words = text.split(" ")
nwords = []
for w in words:
nw = w[::-1]
nwords.append(nw)
return " ".join(nwords)

Mastering the Ceasar shift cipher
kpfkhhgtgpeg yknn egtvckpna dg vjg fqyphcnn qh ocpmkpf, dwv yjq ectgu?
How to crack this?

In-place condition aka ternary operator
• If takes a complete line – sometimes it is too
much
• You can reverse it for in-place condition
a = 4
b = 3
print (a if a > b else b)

Mastering the Ceasar shift cipher
kpfkhhgtgpeg yknn egtvckpna dg vjg fqyphcnn qh ocpmkpf, dwv yjq ectgu?
stoplist = [ ' ', ',', '?']
def ceasar(text, shift):
return "".join([t if (t in stoplist) else chr(ord('a') + (ord(t) - ord('a') + shift + 26) % 26 ) for t in text])

Simple substitution cipher
тhe$e @Яe que$т!0п$ f0Я @cт!0п, п0т $pecu1@т!0п, шh!ch !$ !d1e.
How to optimize replace here?

Dictionary
• Like a usual dictionary
– Has a key – e.g. the glossary word we look for
– Contains value – e.g. the explanation for word
• It helps to associate things pairwise
• Most often used to find a value for a key, but
can be reversed if needed (costy!)
• Other names: hash, hashtable, map

Dictionary operations
1. How to create a d?
2. How to add an
element?
3. How to check for
element?
4. How to retrieve an
element?
1. dct = { ‘a’ : ‘b’, ‘b’ : ‘c’}
2. dct[‘v’] = ‘w’
3. if (elem in dct):
4. dct[‘b’]

Simple substitution cipher
тhe$e @Яe que$т!0п$ f0Я @cт!0п, п0т $pecu1@т!0п, шh!ch !$ !d1e.
def subst(text):
s = { 'т' : 't', '$' : 's', '@' : 'a', '!' : 'i', 'Я' : 'r', '1' : 'l', 'ш' : 'w', '0' : 'o', 'п' : 'n'}
return "".join([t if not(t in s.keys()) else s[t] for t in text ])

BUILDING DECODING SOFTWARE
Total recap

Decoding assistant
> message .eldi si hcihw ,noitaluceps ton ,noitca
rof snoitseuq era esehT
Message [0]: “.eldi si hcihw ,noitaluceps ton
,noitca rof snoitseuq era esehT”
>apply palindrome 0
Message [0]: “sdsdf”
Applied k

CoderDojo: Intermediate Python programming course

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