listcomp

# simply function
old_list = ['this','is','a','man']
new_list = []
for item in old_list:
    if len(item) > 2:
        new_list.append(item[::-1])
print(new_list)        
# list comprehension
# new_list = [expression action, for loop, filter]
new_list = [item[::-1] for item in old_list if len(item) > 2]
print(new_list)        
def temp():
    new_list = []
    for i in range(10):
        new_list.append(i**2)
    return new_list    
x = [i for i in range(1,11)]
print(x)
# gen a list of numbers
new_list = []
for i in range(10):
    new_list.append(i)
print(new_list)   
# list comprehension way
# [i] <= [for i in range(10)]
new_list = [i for i in range(10)]
print(new_list)   
new_list = [i for i in "hello"]
print(new_list)
# gen a list of odd numbers
new_list = []
for i in range(10):
    if (i % 2):
        new_list.append(i)
print(new_list)        
x = [i for i in range(10) if i % 2]
print(x)
# list comprehension way
new_list = [i for i in range(10) if i % 2]
print(new_list)
# nested for loop, we can copy the for loop order
l = []
for i in range(5):
    for j in range(5):
        for k in range(5):
            l.append((i,j,k))
print(l)            
l = [(i,j,k) for i in range(5) for j in range(5) for k in range(5)] 
print(l)
# filter in between for loop
l = []
for i in range(5):
    for j in range(5):
        for k in range(5):
            if i == j:
                l.append((i,j,k))
print(l) 
l = [(i,j,k) for i in range(5) for j in range(5) for k in range(5) if i == j] 
print(l)
l = [(i,j,k) for i in range(5) for j in range(5) if i == j for k in range(5)] 
print(l)
# ex 1
l = []
for i in range(1,6):
    if i % 2 == 0:
        for j in range(1,6):
            if j % 3 == 0:
                l.append((i,j))
print(l)               
x = [(i,j) for i in range(1,6) if i % 2 == 0 for j in range(1,6) if j % 3 == 0]         
print(x)
# ex 2
l = []
for i in range(1,6):
    for j in range(1,6):
        if i % 2 == 0:
            if j % 3 == 0:
                l.append((i,j))
print(l)
x = [(i,j) for i in range(1,6) for j in range(1,6) if i % 2 == 0 and j % 3 == 0]
print(x)
print("ex 3")
# ex 3
for i in range(1,6):
    for j in range(1,6):
        if i % 2 == 0 and j % 3 == 0:
            l.append((i,j))
# l = [(i,j) for i in range(1,6) if j % 3 == 0 for j in range(1,6) if i % 2 == 0] # j is undefined