All the computing is about ones and zeroes

>>> "{0:b}".format(42)
'101010'
        

Meaning:
42 = 1 × 2⁵ + 0 × 2⁴ + 1 × 2³ + 0 × 2² + 1 × 2¹ + 0 × 2⁰

All the computing is about ones and zeroes

>>> list(map(ord, "I🧡∞"))
[73, 129505, 8734]
        

Meaning:
letter "I" is encoded by number 73
emoji "🧡" is encoded by number 129505
symbol "∞" is encoded by number 8734

Memory is taken care of

• memory is sequential, i.e. address #2 follows address #1
• everything is of known length
• if you have some data, it's somewhere in the memory

Memory is taken care of

>>> a = [1,2,3]
>>> b = [1,2,3]
>>> c = a
>>> object.__repr__(a)
'<list object at 0x100c6bf08>'
>>> object.__repr__(b)
'<list object at 0x100cad6c8>'
>>> object.__repr__(c)
'<list object at 0x100c6bf08>'
        

Meaning:
object "a" points to address 0x100c6bf08
object "b" points to address 0x100cad6c8
object "c" points to the same address as object "a"

Python: programming language and a tool

What you downloaded is a python program to run your code written in python language

A program operates in the context of:

• input (variable data)
• output (data, usually depends on the input)
• state (everything else, e.g. file system)

Python as a language

• reads from top to bottom, from left to right
• has sentences, called statements
• has parts of speech
• is hierarchical
• can express same thing in lots of different ways

max_i, max = 0, array[0]
for i, el in enumerate(array[1:]):
    if el > max:
        max_i = i + 1

Coding is a dialogue

Coding is a dialogue

Abstract syntax tree (AST)

1 + 2 * 3 != (1 + 2) * 3

max_i, max = 0, array[0]
for i, el in enumerate(array[1:]):
    if el > max:
        max_i = i + 1

Abstract syntax tree (AST)

Each node does something to the state, and has an output
Python computes bottom-up by nodes.
So:

x = (7 + 2) * 5

x = (9) * 5

Parts of speech, simple

Parts of speech, complex

Expressions, references

Expressions, subscripts

Expressions, operators

Sentence types, aka statemenets

if x > y:
    print("Greater")
elif x < y:
    print("Less")
else:
    print("Equal?")

Sentence types, loops

for item in collection:
    print(item)
else:
    print("the end")

while x > 0:
    x = x - 1
else:
    print("the end")

Sentence types, misc.

try:
    maybe_works()
except Exception as e:
    print("well, it didn't")

import antigravity
import pandas as pd
from matplotlib import pyplot as plt

Sentence types, functions

def index_of_max(array):
    max_i, max = 0, array[0]
    for i, el in enumerate(array[1:]):
        if el > max:
            max_i = i + 1
    return max_i
print(index_of_max([1,2,3]))
print(index_of_max([]))

Errors

EVERYBODY MAKES THEM

Errors

Switch to Errors notebook

Data types

Lists: a collection of different objects

a = []
a.append(1)     # a = [1]
a.extend([2,3]) # a = [1,2,3]
a.reverse()     # a = [3,2,1]
a.index(1)      # 2 -------^
a.pop()         # a = [3,2]
del a[0]        # a = [2]

Data types

Dictionaries: a mapping between keys and values

a = {1:1, 2:4, 3:9, 4:16}
a[5] = 25              # a = {1:1, 2:4, 3:9, 4:16, 5:25}
a.extend({0:0, 1:-1})  # a = {1:-1, 2:4, 3:9, 4:16, 5:25, 0:0}
del a[4]               # a = {1:-1, 2:4, 3:9, 5:25, 0:0}
a.get(1)               # -1
a.pop(2)               # 4; a = {1:-1, 3:9, 5:25, 0:0}
list(a.keys())         # [1, 3, 5, 0]
list(a.values())       # [-1, 9, 25, 0]
list(a.items())        # [(1,-1),(3,9),(5,25),(0,0)]

Other people's code

• distributed as packages (or libraries)
• package has a name and a version
• versions change all the time
• manage packages with pip (or conda)
• work in projects and manage each project's packages independently with pipenv (or virtualenv or conda)

Most common packages:

• numpy: for effective computation and linear algebra
• pandas: for working with data in tables
• matplotlib: for plotting data
• scikit-learn: a collection of machine learning algorithms