Python Zero to Heros

Online Absolute Beginner Python Tutorials 

Every Sunday 1pm (UK time/ BST)

Get this slide deck: bit.ly/PyFlowControl

Recap

Python objects - int, float, str, list, dict, bool

Python functions - append, pop, remove, sum, sort, max, min, len, count

mutable vs hashable

 

Any Questions?

Comparison

>, >=, <, <=, ==, !=

in, is

does not work on None

 

Try this:

a = [1]

b = [1]

a == b

a is b

Boolean (bool)

True, False

need to be capitalised: true, FALSE

logic operations: and, or, not

False includes 0 and '' while True are the rest

 

and: if 1st is False, 2nd Ignore
or: if 1st is True, 2nd Ignore 

If Else

branching, which path to go

if, elif, else

if age < 18:
    sorry_no_beer()
elif age < 25:
    show_id()
else:
    serve_beer()

Sometimes we have to advoid None

parent = "mother" if (gender=="female") else "father"

For loop

looping, doing something again and again

e.g. do the same thing for everthing is a list

my_friends = ["Sandrine", "Emanuil", "Enrica"]
for friend in my_friends:
  print(f"{friend} is my firend.")

e.g. do things 10 times

count = 0
for _ in range(10):
	count = count + 1
print(f"I have done {count} push-ups.")

Range

range(stop) or range(start, stop[, step])

Try these:

for count in range(1, 11):
	print(f"So far, I have done {count} push-ups.")
for count in range(2, 22, 2):
	print(f"I have {count} shoes.")

List Comprehension

A condence way of creating a list via looping.

Instead of doing this:

result = []
for num in range(10):
	result.append(num*2)
print(result)

Do this:

result = [num *2 for num in range(10)]
print(result)

Looping through dict

key-value pairs, {'a': 'apple', 'b': 'banana'}

how_to.keys(), how_to.values(), how_to.items()

For example:

how_to = {1: 'Open the door',
          2:'Put the elephant in',
          3:'Close the door'}
for key, value in how_to.items():
  print(f"Step number {key}, {value}")
sq_num = {num: num**2 for num in range(10)}
print(sq_num)

While Loop

Another way of doing something again and again base on the condition rather then through a sequence of things.

For example:

import random
basket = ["apple", "orange", "pear", "banana", "peach"]
while random.choice(basket) != "banana":
  print("Try again")
print("I have got banana!")

While Loop

break and continue (apply to for loop as well)

break: exit the loop

continue: ignore the rest and start next iteration

import random
basket = ["apple", "orange", "pear", "banana", "peach"]
while True: #DANGER
  choice = random.choice(basket)
  if choice == "banana":
    print("I have got banana!")
    break
  print(f"I got {choice}, try again.")

What if I get everything but oranges?

Let's write some programs

 

1. I randomly pick a fruit from the baskets, I put anything I got in my shopping bag except oranges. I really need some bananas, don't stop till I got one. (random_fruit.py)
 

2. Tom and Matt both have a shopping list, we want to combine them and remove the redundant items, then calculate how much they spend in total at the end. (combine_checkout.py)

 

https://github.com/Cheukting/python02hero/tree/master/2020-04-19-python-control-flow

Homework 📝

 

1. one_number_bingo.py: I can buy a ticket for £3 with one number assigned to me at random. It could be any number from  1 to 999. How much do I have to pay to win the game in one situation?

2.  one_number_bingo.py (bonus): do Monte Carlo similation to get the average money sepnd instead)

 

https://github.com/Cheukting/python02hero/tree/master/2020-04-19-python-control-flow

Next week:
Functions and Modules

Sunday 1pm (UK time/ BST)

There are also Mid Meet Py every Wednesday 1pm

Python Control Flow

By Cheuk Ting Ho

Python Control Flow

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