Coding Fun

  In Python, list support + and += operators. They could do the same thing as the method extend(). extend(): iterate through the iterable object and append each element from the iterable to the end of the list to be extended. Its parameter could be any iterable. >>> a = ['a','b','c'] >>> b = ['x','y','z'] >>> a.extend(b) >>> a ['a', 'b', 'c', 'x', 'y', 'z'] + operator: instead of extending the list in place, it creates a new list leaving original list untouched; it is not as effcient as two others.  >>> a = ['a','b','c'] >>> b = ['x','y','z'] >>> c = a + b >>> c ['a', 'b', 'c', 'x', 'y', 'z'] += operator: it extends the list in place which is the same as the extend() method. >>> a = ['a','b','c

  Python lists are mutable, you can add objects to the list in place. Both append() and extend() methods could do the trick. append(): add a single object to the end of the list >>> l = ['a', 'b', 'c'] >>> l.append(['d','e','f']) >>> l ['a', 'b', 'c', ['d', 'e', 'f']] extend(): add all the elements from the iterable to the end of the list >>> l.extend(['d','e','f']) >>> l ['a', 'b', 'c', 'd', 'e', 'f']

In python, you could use global keyword to declare a variable inside a function as a global variable, such as: >>> global_var = 0 >>> def fun1(): global_var = 10 # global_var as local var print(global_var) >>> def fun2(): global global_var # declare global_var to be a global var global_var = 5 print(global_var) >>> print(global_var) 0 >>> fun1() 10 >>> print(global_var) 0 >>> fun2() 5 >>> print(global_var) 5 We define a global_var outside functions. Inside f un1() we define a local global_var without declaring it as global . Although it has the same name as the global_var outside the function, it is totally isolated from the gobal variable-- global_var . Inside fun2() , we declare global_var as a global variable, so it becomes global .  First, we print global_var , it is 0. Then invoke fun1() , it prints the result of the local variable global_var . We then check the value of global_var , it is sti

 The pythonic way to do this is: l = [] #A empty list is evalutated to False in Python. if not l:      print('list empty')