Python---class and iter

import itertools
import subprocess
import util_m
'''it is for shell command'''
import builtins
'''it is loaded into memory when python module starts'''
class myclass1:
    pass

'''pass means {} in java or c'''

class myclass:
    def __init__(self, max):
        self.max=max

    def __next__(self):
        flib = self.a
        if flib > self.max:
            raise StopIteration
        self.a,self.b= self.b, self.a+self.b
        return flib

    def __iter__(self):
        self.a = 0
        self.b=1
        return self

'''
__init__(self)  means contruction function
self means this in c++
__iter__ is used when for loop start, and return interator of self
__next__ is used when for loop next, when StopIteration happen , for loop quit
'''

'''generator expression=====================, use () , it means generator iterator, not to use others'''
gen1 =  (ord(c) for c in {'E', 'B','S','W'})

'''generator function=========================, return ord(c) every time, it is good use'''
def getord(string1):
    for c in string1:
        yield ord(c)

def per1():
    perm1=itertools.permutations([1,2,3],2)
    list1=list(perm1)
    for item in list1:
        yield item
'''
permutations return iterator
list(iterator) returns list, list is many data
use for loop to get each item
because per1 is util app, it not good to print info here, so return generator object
in caller, we can use for loop to print generator object, no need to call next() because for loop is smart
'''

def group1():
    name=['candy', 'mandy','hebe']
    print(list(itertools.groupby(name, len)))
'''return key, value_list'''

def chain1():
    print(list(range(0,5)))
    print(list(itertools.chain(range(0,5), range(6,10))))
    print(list(zip(range(0,5), range(6,10))))
    '''match util 3, because 9 is the last in latter list'''
    print(list(itertools.zip_longest(range(0,5), range(6,10))))
    '''range(0,5)------0,1,2,3,4. match util 4'''

def trans1():
    table1={ord('A'):ord('B')}
    print('Able'.translate(table1))

def eval1():
    x=5
    eval('1+1')
    print(eval('x*5'))
    print(eval('"A"+"B"'))
    print(eval('__import__("subprocess").getoutput("ls ~/ -l")'))
    subprocess.call(['df','-h'])
    subprocess.call(['uname', '-a'])
'''
eval can calculate the expression in string
but it is not safe, it will be attacked by hacker
'''

def subp1():
    print(subprocess.getoutput('ls ~/ -l'))

def builthello():
    print('hello__builtins__')


if  __name__ == '__main__':
    c1 = myclass(6)
    print(c1.max)
    for n in c1:
        print(n)
    try:
        assert 1>2, 'a is not bigger than b'
    except AssertionError:
        print('I got exception')
    print(next(gen1))
    print(next(gen1))
    gen2=getord({'E','B','S','W'})
    print(next(gen2))
    print(next(gen2))
    for item in per1():
        print(item)

    for item2 in list(itertools.permutations([1,2,3], 2)):
        print(item2)

    print(list(itertools.product('ABC','123')))
    print(list(itertools.combinations('ABC',2)))
    group1()
    chain1()
    trans1()
    eval1()
    subp1()
    __builtins__.__dict__['hello']=builthello
    '''add hello api to __builtins__, to load this api when python module starts'''
    hello()
    util_m.built()
    '''for loop is smart, it can call next automatically'''