Function, generator and class

Function

A function can be seen as executable code blocks, which is reusable. It start with the def keyword, a function name with input parameters, and use return to output values.

• Example

def f(x,y):
    return x*y

f(3,4)

12

• Print a sequence without for loop, a function can return itself

def f(x,y):
    print(x)
    if x < y:
        x = x + 1
        return f(x, y)

f(1,5)

1
2
3
4
5

• Binary search

## binary search : only for sorted array, repeatedly dividing the search interval in half, O(logN)
def binary_search(X, x, l, r):
    if r >= l:
        mid = l + (r - l)//2
        if X[mid] == x:
            return mid
        elif X[mid] > x:
            return binary_search(X, x, l=0, r=mid-1)
        else:
            return binary_search(X, x, l=mid+1, r=len(X))
    else:
        return "Not found!"

A = list(range(10))
binary_search(A, 7, l=min(A), r=max(A))

7

Generator

A generator is an iterator, but we can only iterate over them once. It use yield to return an output instead of return in function.

• Example

def generator_function(a_list):
    for i in a_list:
        yield i
a_list = list(range(10))
gf = generator_function(a_list)

next(gf)

0

next(gf)

1

for i in gf:
    print(i)

2
3
4

• Batch generatora huge data set should be loaded in chunks.

A = list(range(10))
def batch_generator(A, batch_size):
    n = 0
    while True:
        data = A[n*batch_size:(n+1)*batch_size]
        n = n + 1
        if not data:
            break
        yield data

for s in batch_generator(A,2):
    print(s)

[0, 1]
[2, 3]
[4, 5]
[6, 7]
[8, 9]

Class

use class to define a class
object can be another class
__int__ function initialize objects, whenever an instance of a class is created its __init__ method is called
self represents the class, all instance method should start with self in a class.

class Cal(object):
    pi = 3.142

    def __init__(self, radius):
        self.radius = radius

    def area(self):
        return self.pi * (self.radius ** 2)

a = Cal(32)
a.area()

3217.408