Python) Control statements

if

Since there are no brackets like in Java, indentation is very important in the if statement. 

In the example below, you must convert the string type 'n' to an integer. 

n = input('Insert an integer.')
print(type(n))             
n = int(n)                 

if n>=0 :
    print(n, 'is a positive number.')

if n<0:
    print(n, 'is a negative number.')

if ~ else with try~ except

try:
    n = int(input('Insert an integer.'))
    
    if n >= 0:
        print(n, 'is a positive number.')
    else:
        print(n, 'is a negative number.')
    
except:
    print('Please insert numbers only.')

if ~ elif ~ else

In Java, there is else if, whereas in Python it is elif. 

s = int(input('Insert your score.'))

if s >= 90:
    print('A')
elif s >= 80:
    print('B')
elif s >= 70:
    print('C')
elif s >= 60:
    print('C')
else:
    print('F')

 

Loops: for / while 

There is no do ~ while statement in Python. Usually for loops are used a lot.

for loop

for loops are many times used with range() built-in function.

Please refer to my last post if you want to know more about the range() function.

링크

Example1

for i in range(10):             # 0 ~ 9
    print(i+1, 'Cofee and Tea')

for i in range(1, 11):          # 1 ~ 10
    print(i, 'Love in Life')
    
for i in range(1, 11, 1):       # 1 ~ 10   
    print(i, 'Happy days')

Example2 

for i in range(1, 10, 2):
    print(i, end=' ')                   # 1 3 5 7 9
print()

for i in range(1, 10):                  # 1 ~ 9
    print(i, end=' ')                   # 1 2 3 4 5 6 7 8 9
print()

for i in range(10):                     # 0 ~ 9
    print(i, end=' ')                   # 0 1 2 3 4 5 6 7 8 9
print()

for i in range(10, 1, -1):
    print(i, end=' ')                   # 10 9 8 7 6 5 4 3 2

Example3

sum = 0
for i in range(1, 11):              #  1 ~ 10
    sum = sum + i                   # sum += i
    print('1~',i,'=',sum)

print('sum=', sum)

Example4

# Sum of odd numbers
odd = 0
for i in range(1, 101, 2):
    odd += i
print(odd)

# sum of even numbers
even = 0
for i in range(0, 101, 2):
    even += i
print(even);

Example5

It is the same result as Example4, but it is a simpler way with just one for loop. 

odd = even = 0
for i in range(1, 101):                 # 1 ~ 100
    if i%2 == 0:                        # Even 
        even += i
    else:                               # Odd
        odd += i
print('1~100 sum of odd numbers:', odd)
print('1~100 sum of even numbers:', even)

Example6

#Multiplication table with a format() function.

dan = int(input('Insert a number between 1 and 9.'))

print('[',dan,'Table ]')
for i in range(1, 10):              # 1 ~ 9
    # print(dan, '*', i, '=', dan * i)
    print('{0} * {1} = {2}'.format(dan, i, dan*i))

Example7 

for loop with list

# List
list = ['China', 'Canada', 'Egypt', 'South Korea', 'France']
print(type(list))              # <class 'list'>
print(list)                    # ['China', 'Canada', 'Egypt', 'South Korea', 'France']
print(list[0])                 # China

for i in list:
    print(i, end=' ')           # China Canada Egypt South Korea France
print()

for loop with tuple

#Tuple
t = ('red','orange','yellow','green','blue','navy','purple')
print(type(t))                  # <class 'tuple'>
print(t)                        # ('red', 'orange', 'yellow', 'green', 'blue', 'navy', 'purple')
print(t[0])                     # red

for i in t:
    print(i, end=' ')           # red orange yellow green blue navy purple
print()

for loop with dictionary

# Dictionary : { 'key' : 'value' }
dic = {'Apple' : 'http://www.apple.com',
       'Google' : 'http://www.google.com',
       'Naver' : 'http://www.naver.com'}

print(type(dic))                # <class 'dict'>
print(dic)                      # {'Apple': 'http://www.apple.com', 'Google': 'http://www.google.com', '네이버': 'http://www.naver.com'}
print(dic['Apple'])             # http://www.apple.com

for k, v in dic.items():
    print(k,':', v)

while loop

while loop is very similar to Java.

Example1 

i = 1                          
while i <= 10 :                
    print(i,'I love Python')           
    i += 1

Example2

i=1; odd=even=0                
while i <= 100:                # Condition
    if i%2 == 0:                # Even numbers
        even += i
    else:                       # Odd numbers
        odd += i
    i += 1                      

print('1~100 sum of odd numbers:',  odd)
print('1~100 sum of even numbers:',  even)

Example3

Multiplication table with format function.

dan = int(input('Insert a number between 1 to 9'))

i = 1                                  
while  i <= 9:                          
    # print(dan, '*', i, '=', dan*i)
    print('{0} * {1} = {2}'.format(dan, i, dan*i))
    i += 1

Example4

Multiplication table

dan=2                                     
while dan <= 9:                             
    print('[',dan,'Table ]')
    i = 1
    while i <= 9:                           
        print(dan, '*', i, '=', dan*i)
        i += 1                              
    dan += 1                              
    print()

break and continue

Infinite loop 

i=1
while True:

    print(i, 'Infinite loop')
    i += 1

Infinite loop with break

i=1
while True:

    print(i, 'Infinite loop')
    if i == 100: break
    i += 1

for, if, and break

for i in range(1, 1001):            # 1 ~ 1000
    print(i,'Print')

    if i==100:
        print('Loop Escaped')
        break

continue

continue is for going back to the loop. 

Example1 

for i in range(1, 11):              # 1 ~ 10

    if i==5:
        continue
    print(i, 'Print')

Example2 

If it is not divided into 5, it skips printing.

for i in range(1, 101):             # 1 ~ 100

    if i%5 != 0:                    
        continue
    print(i)