Python: Iteration

Given a list or tuple, we can iterate through for the list or tuple through a loop, which we call an iteration (iteration).

In Python, iterations are for ... in done through, and in many languages such as C, the iteration list is done by subscript, such as Java code:

 for (i=0; i<list.length; i++) {    = list[i];}

As you can see, Python's for loop is more abstract than the C for loop, because the Python for loop can be used not only on a list or a tuple, but also on other objects that can iterate.

List this data type although there is subscript, but many other data types are not subscript, but as long as the object can be iterated, whether or not subscript, can iterate, such as dict can iterate:

>>> d = {'a'b' 'C': 3 } for in D: ...      Print (Key) ... ACB

Because Dict storage is not ordered in list order, the resulting order of the iterations is likely to be different.

By default, the Dict iteration is key. If you want to iterate over value, you can use for value in d.values() it if you want to iterate both key and value at the same time for k, v in d.items() .

Because a string is also an iterative object, it can also be used for for loops:

 for inch ' ABC ' :...      Print (CH) ... ABC

So, when we use for a loop, the loop works as long as it works on an iterative object, for and we don't care much about whether the object is a list or another data type.

So, how can you tell if an object is an iterative object? The method is judged by the iterable type of the collections module:

 from Import iterable>>> isinstance ('abc'#  str can iterate True  #  Whether the list can iterate True#  integer Whether it can iterate False

The last small question, what if I want to implement a Java-like subscript loop on the list? Python's built-in enumerate functions can turn a list into an index-element pair so that the for index and the element itself can be iterated at the same time in the loop:

 for  in Enumerate (['A''B''C' ]):...      Print (i, value) ... 0 A1 B2 C

The above for loop, which references two variables at the same time, is common in python, such as the following code:

 for inch [(1, 1), (2, 4), (3, 9)]: ...      Print (x, y) ... 1 12 43 9

Python: Iteration