Week 1 class demo

This is a copy of what I demonstrated in class when this was first run.

import this

The Zen of Python, by Tim Peters

Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.
Special cases aren't special enough to break the rules.
Although practicality beats purity.
Errors should never pass silently.
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
There should be one-- and preferably only one --obvious way to do it.
Although that way may not be obvious at first unless you're Dutch.
Now is better than never.
Although never is often better than *right* now.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.
Namespaces are one honking great idea -- let's do more of those!

Variables

things about variables

x = 1

print(x * x)

1

print(type(x))

x = x * 100
print(x)

100

phrase = "no semicolons needed!"

print("You said " + phrase)

You said no semicolons needed!

# strings

print('hello', "hello")

hello hello

print("""hello there
there are newlines here
this is valid""")

hello there
there are newlines here
this is valid

text = """hello there
there are newlines here
this is valid"""

text

'hello there\nthere are newlines here\nthis is valid'

3

3

type(3)

int

type(3.0)

float

print(3 * 6)

18

print(3 * 6.0)

18.0

print(234567897654345678987654567897654 * 34656789876)

8129370340661731474943692757700569751350904

text = "3.0"

float(text)

3.0

text = "3"
int(text)

3

int(3.9)

3

int("3.9")

ValueError                                Traceback (most recent call last)

<ipython-input-31-05f4ebb5ab90> in <module>
----> 1 int("3.9")


ValueError: invalid literal for int() with base 10: '3.9'

str(3.99999999)

'3.99999999'

print()

$39.99

print("$" + str(39.99))

$39.99

print(3, 9, 9)

3 9 9

isinstance("hello", str)

True

isinstance("hello", int)

False

isinstance(3.99, (int, float))

True

type("hello") == str

True

type("hello") == int

False

type(3.99) == str

False

try:
    print("hello")
    x = int("4.9")
except:
    print("failure")

hello
failure

num = "3.9"

try:
    num = float(num)
except:
    print("oops")

num

3.9

text = "009939"

print(text.isdigit())
print(text.isnumeric())

True
True

print('二百三'.isdigit())

False

print('二百三'.isnumeric())

True

print('௩௰௭'.isnumeric())

True

l = []

type(l)

list

lista = [1, 2, 3, 4]
listb = ['c', 'p', 'w']
listc = ['d', 1, [], 9, 23.99]

lista.append(5)

lista

[1, 2, 3, 4, 5]

id(lista)

139878782947272

id(listb)

139878782946952

id(listc)

139878782978504

listd = lista

lista

[1, 2, 3, 4, 5]

listd

[1, 2, 3, 4, 5]

listd.append(6)

listd

[1, 2, 3, 4, 5, 6]

lista

[1, 2, 3, 4, 5, 6]

id(lista)

139878782947272

id(listd)

139878782947272

liste = lista[:]

id(lista)

139878782947272

id(liste)

139878782977992

lista

[1, 2, 3, 4, 5, 6]

lista.append(1)
lista.append(1)
lista.append(1)
lista.append(1)

lista

[1, 2, 3, 4, 5, 6, 1, 1, 1, 1]

lista.count(1)

5

lista.index(1)

0

lista.remove(1)

lista

[2, 3, 4, 5, 6, 1, 1, 1, 1]

lista.index(1)

5

lista.index(6)

4

lista[6]

1

type(lista[6])

int

lista

[2, 3, 4, 5, 6, 1, 1, 1, 1]

listb  #start:stop:step

['c', 'p', 'w']

listb.append('z')
listb.append('i')
listb.append('e')

listb

['c', 'p', 'w', 'z', 'i', 'e']

listb[2]

'w'

listb[2:5]

['w', 'z', 'i']

"hello"[2:4]

'll'

listb

['c', 'p', 'w', 'z', 'i', 'e']

listb[-5:-3]

['p', 'w']

listb[-1]

'e'

[listb[-1]]

['e']

listb

['c']

for iterable_variable in sequence: do stuff...

listb

['c', 'p', 'w', 'z', 'i', 'e']

for item in lista:
    print(item)

2
3
4
5
6
1
1
1
1

for aoeuidht in "hello world":
    print(aoeuidht)

h
e
l
l
o

w
o
r
l
d

for i in 30:
    print(i)

TypeError                                 Traceback (most recent call last)

<ipython-input-130-b9ed12485d49> in <module>
----> 1 for i in 30:
      2     print(i)


TypeError: 'int' object is not iterable

print(aoeuidht)

d

data = "haouh"

for data in data:
    print(data)

h
a
o
u
h

data

'h'

text = "hello world"
another = "snake socks"

for i in range(len(text)):
    a = text[i]
    b = another[i]
    print(a + b)

hs
en
la
lk
oe

ws
oo
rc
lk
ds

listc

['d', 1, [], 9, 23.99]

TypeError                                 Traceback (most recent call last)

<ipython-input-141-aee044fbcb2d> in <module>
      1 for item in listc:
----> 2     item + "d"


TypeError: unsupported operand type(s) for +: 'int' and 'str'

listc

['d', 1, [], 9, 23.99]

len(listc)

5

count = 0

for item in listc:
    # do stuff
    #count = count + 1
    count += 1

print(count)

5

lista

[2, 3, 4, 5, 6, 1, 1, 1, 1]

sum(lista)

24

sum(lista) / len(lista)

2.6666666666666665

total = 0

for item in lista:
    # do stuff
    total += item

print(total)

24

base = ""

for item in listc:
    text = str(item)
    base += text

print(base)

d1[]923.99

lista

[2, 3, 4, 5, 6, 1, 1, 1, 1]

listb

['c', 'p', 'w', 'z', 'i', 'e']

lista + listb

[2, 3, 4, 5, 6, 1, 1, 1, 1, 'c', 'p', 'w', 'z', 'i', 'e']

newlist = lista + listb + listc

base = []

for item in newlist[::2]:
    # do stuff
    base.append(item)

print(base)

[2, 4, 6, 1, 1, 'p', 'z', 'e', 1, 9]

print(1 < 3)

True

True

True

False

False

if bool_expression:
    # do this
else: 
    # do that

if "c".isdigit():
    print("this is a digit")
elif "c".isnumeric():
    print("this in numeric")
elif "c".isupper():
    print("is uppcase")
elif "c".islower():
    print("is lowercase")
else:
    print("not a digit")

is lowercase

if "c".isdigit():
    print("this is a digit")

lista

[2, 3, 4, 5, 6, 1, 1, 1, 1]

assert len(lista) == 9

lista.pop(2)

4

assert len(lista) == 9

AssertionError                            Traceback (most recent call last)

<ipython-input-173-37678435df7c> in <module>
----> 1 assert len(lista) == 9


AssertionError: