Python Many From Learn By Example Github

Question 1

_

Answer 1

Refers to previous result

3*7
21

_*2
42

Question 2

Division without remainder , modulo

Answer 2

//

33//10
3

32 % 10
2

Question 3

Multi line string

Answer 3

triple_quotes.py

print(‘'’hi there.
how are you?’’’)

Question 4

r strings

Answer 4

print(r’item\tquantity’)
item\tquantity

r’item\tquantity’
‘item\tquantity’

Question 5

f strings

Answer 5

restricting number of digits after the decimal point

str1 = ‘hello’
str2 = ‘ world’
f’{str1}{str2}’
‘hello world’

f’{str1}({str2 * 3})’
‘hello( world world world)’

appx_pi = 22 / 7

f’Approx pi: {appx_pi:.5f}’
‘Approx pi: 3.14286’

f’{appx_pi:.3f}’
‘3.143’

f’{32 ** appx_pi:.2e}’
‘5.38e+04’

Question 6

Type

Answer 6

num = 42
type(num)
<class ‘int’>

type(22 / 7)
<class ‘float’>

type(‘Hi there’)
<class ‘str’>

Question 7

And or not

Answer 7

Lowercase

4 > 3.14 and 2 <= 3
True

hi’ == ‘Hi’ or 0 != ‘0’
True

not ‘bat’ < ‘at’
True
num = 0
not num
True

Question 8

Ifelse one line

Answer 8

def absolute(num):
return num if num >= 0 else -num

Question 9

Continue

Answer 9

for num in range(10):
… if num % 3:
… continue
… print(f’{num} * 2 = {num * 2}’)
…
0 * 2 = 0
3 * 2 = 6
6 * 2 = 12
9 * 2 = 18

Question 10

Sampling/ random

Answer 10

rand_number.py

import random

gives back an integer between 0 and 10 (inclusive)
rand_int = random.randrange(11)

Question 11

Variable taking name depending on program calling it

Answer 11

The special variable __name__ will be assigned the string value ‘__main__’ only for the program file that is executed. The files that are imported inside another program will see their own filename (without the extension) as the value for the __name__ variable.

An example of a dunder variable

Question 12

Try except

Answer 12

try_except.py

from math import factorial

while True:
try:
num = int(input(‘Enter a positive integer: ‘))
print(f’{num}! = {factorial(num)}’)
break
except ValueError:
print(‘Not a positive integer, try again’)

Using as:

try:
num = 5 / 0
except ZeroDivisionError as e:
print(f’oops something went wrong! the error msg is:\n”{e}”’)

oops something went wrong! the error msg is:
“division by zero”

Question 13

Try except else, and also finally

Answer 13

try_except_else.py

while True:
try:
num = int(input(‘Enter an integer number: ‘))
except ValueError:

Finally happens no matter what

try:
num = int(input(‘Enter a positive integer: ‘))
if num < 0:
raise ValueError
except ValueError:
print(‘Not a positive integer, run the program again’)
else:
print(f’Square root of {num} is {num ** 0.5:.3f}’)
finally:
print(‘\nThanks for using the program, have a nice day’)

    print('Not an integer, try again')
else:
    print(f'Square of {num} is {num ** 2}')
    break

Question 14

Raise

Answer 14

def sum2nums(n1, n2):
… types_allowed = (int, float)
… if type(n1) not in types_allowed or type(n2) not in types_allowed:
… raise TypeError(‘Argument should be an integer or a float value’)
… return n1 + n2
…
sum2nums(3.14, -2)
1.1400000000000001
sum2nums(3.14, ‘a’)
Traceback

Question 15

Check something true

Answer 15

Assert 2<5

Question 16

join paths

Answer 16

os.path.join(workdir,”hello.txt”)

Question 17

enumerate

Answer 17

for index, item in enumerate(L):

Question 18

run command after creating it, metaprogramming

Answer 18

execstring = ‘assert ‘ + astring + “,’” + astring + “’”
exec(execstring)

setattr might be helpful also

Question 19

create empty list

Answer 19

l = [None] * 10
l
[None, None, None, None, None, None, None, None, None, None]

Question 20

any, all

Answer 20

any(iterable)
Return True if any element of the iterable is true. If the iterable is
empty, return False. Equivalent to
all all
all(iterable)
Return True if all elements of the iterable are true (or if the iterable
is empty).

Question 21

flatten list

Answer 21

using a listcomp with two ‘for’
vec = [[1,2,3], [4,5,6], [7,8,9]]
[num for elem in vec for num in elem]
[1, 2, 3, 4, 5, 6, 7, 8, 9]

Question 22

Tuple declarations

Answer 22

can also use: empty_tuple = tuple()

empty_tuple = ()

note the trailing comma, otherwise it will result in a ‘str’ data type
# same as ‘apple’, since parentheses are optional here
one_element = (‘apple’,)

multiple elements example
dishes = (‘Aloo tikki’, ‘Baati’, ‘Khichdi’, ‘Makki roti’, ‘Poha’)

mixed data type example, uses expressions as well
mixed = (1+2, ‘two’, (-3, -4), empty_tuple)
mixed
(3, ‘two’, (-3, -4), ())

Question 23

Tuple from iterable

Answer 23

chars = tuple(‘hello’)
chars
(‘h’, ‘e’, ‘l’, ‘l’, ‘o’)
tuple(range(3, 10, 3))
(3, 6, 9)

Question 24

Indexing from end

Answer 24

len(primes) - 1 = 4, so this is same as primes[4]

primes = (2, 3, 5, 7, 11)

primes[-1]
11

primes[-1:]
(11,)
primes[-2:]
(7, 11)

Question 25

Copy

Answer 25

import copy
new_list = copy.deepcopy(old_list)

Question 26

Step sizes, and reverse order

Answer 26

same as primes[0:5:2]

primes = (2, 3, 5, 7, 11)

primes[::2]
(2, 5, 11)

# note that the element at index 1 (stop value) isn’t part of the output
primes[3:1:-1]
(7, 5)
# reversed sequence
# would help you with the palindrome exercise from Control structures chapter
primes[::-1]
(11, 7, 5, 3, 2)

Question 27

Unpacking with *

Answer 27

values = (‘first’, 6.2, -3, 500, ‘last’)

x, *y = values
x
‘first’
y
[6.2, -3, 500, ‘last’]

a, *b, c = values
a
‘first’
b
[6.2, -3, 500]
c
‘last’

Question 28

Tuples preferred way to return multiple values

Answer 28

def min_max(iterable):
… return min(iterable), max(iterable)
…
min_max(‘visualization’)
(‘a’, ‘z’)
small, big = min_max((10, -42, 53.2, -3))
small
-42
big
53.2

Question 29

Varying number of args

Answer 29

def sum_nums(*args):
… total = 0
… for n in args:
… total += n
… return total
…
sum_nums()
0
sum_nums(3, -8)
-5
sum_nums(1, 2, 3, 4, 5)
15

Question 30

Iterate over two variables at the same time

Answer 30

odd = (1, 3, 5)
even = (2, 4, 6)
for i, j in zip(odd, even):
… print(i + j)
…
3
7
11

Question 31

Get attributes

Answer 31

dir(x), or dir(tuple)

Question 32

Count instances in a tuple

Answer 32

nums = (1, 4, 6, 22, 3, 5, 2, 1, 51, 3, 1)
nums.count(3)
2
nums.count(31)
0

Question 33

List assignment not intuitive to me

Answer 33

list will automatically shrink/expand as needed

nums[1:4] = [2000]
nums
[100, 2000, -2, -3]
nums[1:2] = [3.14, 4.13, 6.78]
nums
[100, 3.14, 4.13, 6.78, -2, -3]

Question 34

remove things from lists

Answer 34

mylist = [4, 6, 8]
mylist.pop(2)
8
mylist

mylist = [4, 6, 8]
del mylist[1]
mylist
[4,8]

mylist = [4, 6, 8]
del mylist[-1]
mylist
[4,6]

remove uses the value, not the index
mylist = [4, 6, 8]
mylist.remove(6)
mylist
[4,8]

Question 35

replace multiple values of a list with one value

Answer 35

a = [0,1,2]
a[:2]=[-1]*2
a
[-1, -1, 2]

a[:2]=-1 does not work

Question 36

if else one line

Answer 36

isApple = True if fruit == ‘Apple’ else False

Question 37

F strings

Answer 37

balance = 5425.9292
f”Balance: ${balance:.2f}”
‘Balance: $5425.93’

heading = “Centered string”
f”{heading:=^30}”
‘=======Centered string========’

In the second example, you use the :=^30 format specifier. In this case, you’re telling .format() to format the input value using the = symbol as a filler character. The ^ symbol centers the input value by inserting = symbols on both sides to reach thirty characters.

Real Python

Question 38

F strings with equals sign

Answer 38

variable = “hello”

print(f”{variable = }”)
variable = ‘hello’

Don’t need the spaces, but probably nine to have.

Question 39

** and args

Answer 39

def many(**kwargs):
… print(f’{kwargs = }’)

many()
kwargs = {}

many(num=5)
kwargs = {‘num’: 5}

many(car=5, jeep=25)
kwargs = {‘car’: 5, ‘jeep’: 25}

Question 40

**and dictionary

Answer 40

Can pass arguments with
**mydict

def greeting(phrase=’hello’, style=’=’):
… print(f’{phrase:{style}^{len(phrase)+6}}’)
…
greeting()
===hello===

mydict = {‘style’: ‘-‘, ‘phrase’: ‘have a nice day’}

greeting(**mydict)
—have a nice day—

Question 41

Set

Answer 41

duplicates are automatically removed

empty_set = set()

empty_set
set()

Declare with braces, items separated by connas

nums = {-0.1, 3, 2, -5, 7, 1, 6.3, 5}
# note that the order is not the same as declaration

nums
{-0.1, 1, 2, 3, 5, 6.3, 7, -5}

set([3, 2, 11, 3, 5, 13, 2])
{2, 3, 5, 11, 13}

set(‘initialize’)
{‘a’, ‘n’, ‘t’, ‘l’, ‘e’, ‘i’, ‘z’}

Question 42

Set operations

Answer 42

union of two sets: color_1 | color_2

color_1 = {‘teal’, ‘light blue’, ‘green’, ‘yellow’}
color_2 = {‘light blue’, ‘black’, ‘dark green’, ‘yellow’}

color_1.union(color_2)
{‘light blue’, ‘green’, ‘dark green’, ‘black’, ‘teal’, ‘yellow’}

color_1.intersection(color_2)
{‘light blue’, ‘yellow’}

color_1.difference(color_2)
{‘teal’, ‘green’}

color_2.difference(color_1)
{‘dark green’, ‘black’}

# i.e. union of previous two operations: color_1 ^ color_2
color_1.symmetric_difference(color_2)
{‘green’, ‘dark green’, ‘black’, ‘teal’}

Question 43

Change sets in place and add elements

Answer 43

union

Methods like add(), update(), symmetric_difference_update(), intersection_update() and difference_update() will do the modifications in-place.

color_1 = {‘teal’, ‘light blue’, ‘green’, ‘yellow’}
color_2 = {‘light blue’, ‘black’, ‘dark green’, ‘yellow’}

color_1.update(color_2)
color_1
{‘light blue’, ‘green’, ‘dark green’, ‘black’, ‘teal’, ‘yellow’}

color_2.add(‘orange’)
color_2
{‘black’, ‘yellow’, ‘dark green’, ‘light blue’, ‘orange’}

Question 44

API endpoints

Answer 44

Specific site on an API site, e.g. /routes to get routes for where to go.

Question 45

API request and status code

Answer 45

myparams = {“param1”: 42, “param2”: 51}
response = requests.get(“http://some.api.com/someinfo.json”, params=myparams)

status_code = response.status_code
print(response.content)
json_data = response.json()