---
id: practical-python-6.1
source_exercise_id: "6.1"
title: "Iteration Illustrated"
section: "6.1 Iteration Protocol"
source_path: "06_Generators/01_Iteration_protocol.md"
source_repo: "https://github.com/dabeaz-course/practical-python"
source_commit: "93dca856b41c61a0a0f85ae334116e4c125629ea"
student_visible_solution: false
has_private_solution: false
skip: false
---

# Exercise 6.1: Iteration Illustrated

> Source: Practical Python Programming, `06_Generators/01_Iteration_protocol.md`.

### Exercise 6.1: Iteration Illustrated

Create the following list:

```python
a = [1,9,4,25,16]
```

Manually iterate over this list.  Call `__iter__()` to get an iterator and
call the `__next__()` method to obtain successive elements.

```python
>>> i = a.__iter__()
>>> i
<listiterator object at 0x64c10>
>>> i.__next__()
1
>>> i.__next__()
9
>>> i.__next__()
4
>>> i.__next__()
25
>>> i.__next__()
16
>>> i.__next__()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration
>>>
```

The `next()` built-in function is a shortcut for calling
the `__next__()` method of an iterator. Try using it on a file:

```python
>>> f = open('Data/portfolio.csv')
>>> f.__iter__()    # Note: This returns the file itself
<_io.TextIOWrapper name='Data/portfolio.csv' mode='r' encoding='UTF-8'>
>>> next(f)
'name,shares,price\n'
>>> next(f)
'"AA",100,32.20\n'
>>> next(f)
'"IBM",50,91.10\n'
>>>
```

Keep calling `next(f)` until you reach the end of the
file. Watch what happens.

## 关联来源

- [[summaries/01_Iteration_protocol]]