[TIL] Python Basic Review

Operator

 print(10 // 3) # quotient - 3
 print(10 % 3) # remainder - 1
 print(10 ** 2) # exponential - 100

String

 str1 = 'Hello'
 str2 = "World!"
 print(len(str1))
 print(str1 + ' ' + str2)

 # String Methods
 sentence = 'Python is FUN!!'
 email = 'siwon@naver.com'

 print(sentence.upper())
 print(sentence.lower())

 print(email.split('@')[1].split('.')) # return list

 print(sentence.replace('!', ':)'))

 # f-string
 names = ['Tom', 'David', 'Alice']
 for name in names:
     print(f'My name is {name}.')

 # Indexing and Slicing
 f = 'abcdefghijkl'
 print(f[1])

 print(f[4:15]) # f[4] ~ f[14]
 print(f[8:]) # f[8] ~ end
 print(f[:7]) # front ~ f[6]
 print(f[:]) # everything

List

 a = [3, "a", 6, True, [2, 3]] # order matters & data type convertible
 print(len(a))
 empty = []
 empty = list()

 print(a[1:3])
 print(a[-1]) # last index value
 print(a[4][0])

 # List Methods
 a = [1, 2, 3]
 a.append(4)
 a.append([5, 6])
 a += [7, 8]
 print(a)

 b = [5, 2, 1]
 b.sort() # ascending
 print(b)
 b.sort(reverse=True) # descending
 print(b)

 print(1 in b)
 print("1" not in a)

Dictionary

 person = {"name": "Bob", "age": 21}
 print(person["name"])

 empty = {}
 empty = dict()

 print(person[0]) # ERROR: dict has no order => no indexing

 # update dictionary 
 person["name"] = "Robert"

 # add (key, value)
 person["height"] = 174.8
 person["score"] = {"math": 81, "science": 90, "English": 100}
 print(person["score"]["math"])

 # check existance
 print("name" in person)
 print("email" not in person)

 # List and dictionary
 people = [{'name': 'Bob', 'age': 21}, {'name': 'Alice', 'age': 25}]

 print(people[0]['name'])

 person = {'name': 'Tom', 'age': 19} 
 people.append(person)
 print(people[2]['name'])

For Loop

 people = [
     {'name': 'bob', 'age': 20},
     {'name': 'carry', 'age': 38},
     {'name': 'john', 'age': 7},
     {'name': 'smith', 'age': 17},
     {'name': 'ben', 'age': 27},
     {'name': 'bobby', 'age': 57},
     {'name': 'red', 'age': 32},
     {'name': 'queen', 'age': 25}
 ]

 for person in people:
     if person['age'] > 20:
         print(person['name'])

 fruits = ['orange', 'apple', 'banana', 'pear', 'watermelon']

 for i, fruit in enumerate(fruits):
     print(i, fruit)
     if i == 4: # printing only first 5 values
         break

Function

 def check_gender(pin):
     num = int(pin.split('-')[1][0])
     if num % 2 == 0:
         print('W')
     else:
         print('M')

 my_pin = "001108-1202302"
 check_gender(my_pin)

Tuple

 # Tuple - immutable, order matters
 a = (1, 2, 3)
 print(a[0])
 # a[0] = 99 - not acceptable
 a_dict = [('Bob', 21), ('Alice', 25), ('Tom', 19)]
 print(a_dict)

Set

 # Set - no duplicates
 a = [1,2,3,4,5,3,4,2,1,2,4,2,3,1,4,1,5,1]
 a_set = set(a)
 print(a_set)

 a = set(['apple', 'banana', 'strawberry'])
 b = set(['apple', 'melon'])
 print(a & b) # intersection
 print(a | b) # union
 print(a - b) # except

Error Handling: Try-Except Statement

 people = [
     {'name': 'bob', 'age': 20},
     {'name': 'carry', 'age': 38},
     {'name': 'john', 'age': 7},
     {'name': 'smith', 'age': 17},
     {'name': 'ben', 'age': 27},
     {'name': 'bobby'},
     {'name': 'red', 'age': 32},
     {'name': 'queen', 'age': 25}
 ]

 for person in people:
     try:
         if person['age'] > 18:
             print(person['name'])
         else:
             print(f'{name} - minor')
     except:
         name = person['name']
         print(f'{name} - error')

File Import

# main_func.py
def say_hi():
    print('Hi!')

# main.py
from main_func import *

say_hi()

Ternary Operators

num = 3

if num % 2 == 0:
    result = 'even'
else:
    result = 'odd'
print(f'{num} is {result}')
#-----------------------------------------
result = 'even' if num % 2 == 0 else 'odd' # ternary
print(f'{num} is {result}')

a_list = [1, 3, 2, 5, 1, 2]
b_list = []

for a in a_list:
    b_list.append(a * 2)
print(b_list)
#-----------------------------------------
b_list = [a * 2 for a in a_list]
print(b_list)

Map, Filter, and Lambda

# map - manipulate the elements in list
# 1
def check_adult1(person):
    if person['age'] > 18:
        return 'adult'
    else:
        return 'minor'

result1 = map(check_adult1, people)
print(list(result1)) # ['adult', 'adult', 'minor', 'minor', 'adult', 'adult', 'adult', 'adult']

# 2
def check_adult2(person):
    return 'adult' if person['age'] > 18 else 'minor'

result2 = map(check_adult2, people)
print(list(result2))

# 3 - lambda
result3 = map(lambda x: ('adult' if x['age'] > 20 else 'minor'), people)
print(list(result3))

# filter
result = filter(lambda x: x['age'] > 18, people)
print(list(result))

Function Arguments

# 1
def cal(a, b):
    return a + 2 * b

print(cal(3, 5)) # 13
print(cal(5, 3)) # 11
print(cal(a=3, b=5)) # 13
print(cal(b=5, a=3)) # 13

def cal2(a, b=3): # setting default value
    return a + 2 * b

print(cal2(4))
print(cal2(4, 2))
print(cal2(a=6))
print(cal2(a=1, b=7))

# 2
def call_names(*args): # no limit in the number of arguments
    for name in args:
        print(f'{name} is called')
call_names('Tom', 'David', 'Alice')

# 3
def get_kwargs(**kwargs): # no limit in the number of keyword arguments
    print(kwargs)

get_kwargs(name='bob')
get_kwargs(name='john', age='27')

Class

class Monster():
    hp = 100
    alive = True

    def damage(self, attack):
        self.hp = self.hp - attack
        if self.hp < 0:
            self.alive = False

    def status_check(self):
        if self.alive:
            print('Alive!')
        else:
            print('Dead...')

m1 = Monster()
m1.damage(120)

m2 = Monster()
m2.damage(90)

m1.status_check()
m2.status_check()