파이썬 Basic - 조건문/반복문

1. 조건문 - if

• if 조건:
  elif 조건:
  else:

a = 1

if a > 0:
    print('a == ',a)
elif a == 0:
    print('a == ', a)
else:
    print('a == ', a)
    

a == 1

list_data = [10, 20, 30, 40, 50]
dict_data = {'key1':1, 'key2':2}

if 45 in list_data:
    print("45 is in list_data")
else:
    print("45 is not in list_data")
    
if 'key1' in dict_data:
    print("key1 is in dict_list")
else:
    print("key1 is not in dict_list")

45 is not in list_data
key1 is in dict_list

---

2. 반복문 - for

• for variable in range(...):
• for variable in list, dict...:

#range()함수는 시작값~마지막값-1
for data in range(10):
    print(data, end=' ')
    
print()

for data in range(11,20):
    print(data, end=' ')
    
print()

for data in range(0, 10, 2): #0부터 10-1까지 2씩 증가
    print(data, end=' ')

0 1 2 3 4 5 6 7 8 9
11 12 13 14 15 16 17 18 19
0 2 4 6 8

list_data = [10, 20, 30, 40, 50]
dict_data = {'key1':1, 'key2':2}

for data in list_data:
    print(data, end=' ')

print()
for data in dict_data:
    print(data, end=' ')
    
print()
for key, value in dict_data.items():
    print(key, value)

10 20 30 40 50
key1 key2
key1 1
key2 2

---

2. 반복문 - list comprehension

• 리스트의 [...]괄호 안에 for 루프를 사용하여 반복적으로 표현식을 실행해서 리스트 요소들을 정의하는 방법
• 머신러닝 코드에서 자주 사용됨.

list_data = [x**2 for x in range(5)]
print(list_data)

[0, 1, 4, 9, 16]

raw_data = [[1,10], [2,15],[3,30],[4,55]]
all_data = [x for x in raw_data]
x_data = [x[0] for x in raw_data]
y_data = [x[1] for x in raw_data]

print("all_data = ",all_data)
print("x_data = ", x_data)
print("y_data = ", y_data)

all_data = [[1, 10], [2, 15], [3, 30], [4, 55]]
x_data = [1, 2, 3, 4]
y_data = [10, 15, 30, 55]

even_number =[]
for data in range(10):
    if data % 2 == 0:
        even_number.append(data)
print(even_number)

[0, 2, 4, 6, 8]

---

3. 반복문 - while, break, continue

• while
• break, continue

data = 5

while data >=0:
    print("data ==", data)
    data -=1

data == 5
data == 4
data == 3
data == 2
data == 1
data == 0

data = 5

while data >= 0:
    print("data ==", data)
    data -= 1
    
    if data == 2:
        print("🎃break here")
        break
    else:
        print("continue here")
        continue

data == 5
continue here
data == 4
continue here
data == 3
🎃break here