[Python] - Powerful Function

1. Range

---

• range는 range(start, end, step) Option
• range's result  start_number ~ end-1 collection

list(range(5,10))
> [5, 6, 7, 8, 9]
list(range(10,20,2))
> [10, 12, 14, 16, 18]

 

2. Enumerate

---

• Use repeat Loop we need to check times Loop
• return tuple( index , element )

for i, v in enumerate(t):
    print("index : {}, value: {}".format(i,v))
"""
index : 0, value: 1
index : 1, value: 5
index : 2, value: 7
index : 3, value: 33
index : 4, value: 39
index : 5, value: 52
"""

 

3. Map

---

map(function, iterable)

 

• map is function that processes the elements of a list as a specified function
• map do not change origin list and create new list

# change float to int
a = [1.2, 2.5, 3.7, 4.6]
a = [int(i) for i in a ]

# map function
a = list(map(int,a))

# int+1
list(map(lambda x:int(x)+1 , a))

 

4. Filter

---

filter(function, iterable)

• filter function return Elements filtered under certain conditions to iterator object

a = [1,2,3,4]
# filter function
result = list(filter(lambda x : x%2==0 , a))

 

5. Zip

---

• zip function get parameter iterable object and returns iterator that can sequentially access each iterable object element 
• Iterate over several iterables in parallel, producing tuples with an item from each one.
• you should be aware of iterable element length. ( the data is woven based on the shortest argument, and the rest is discarded )

numbers = [1, 2, 3]
letters = ["A", "B", "C"]
[pair for pair in zip(numbers, letters) ]
> [(1, 'A'), (2, 'B'), (3, 'C')]

#dict example
keys = [1, 2, 3]
values = ["A", "B", "C"]
dict(zip(keys, values))

# be careful
numbers = ["1", "2", "3"]
letters = ["A"]
list(zip(numbers, letters))
> [('1', 'A')]

 

6. Divmod

---

• divmod function return quotient , remainder 
• if you use low number, divmod is slower than // , % operator ( https://stackoverflow.com/questions/30079879/is-divmod-faster-than-using-the-and-operators )

q, r = divmod(n, d)
q, r = (n // d, n % d)