---
id: practical-python-6.4
source_exercise_id: "6.4"
title: "A Simple Generator"
section: "6.2 Customizing Iteration"
source_path: "06_Generators/02_Customizing_iteration.md"
source_repo: "https://github.com/dabeaz-course/practical-python"
source_commit: "93dca856b41c61a0a0f85ae334116e4c125629ea"
student_visible_solution: false
has_private_solution: false
skip: false
---

# Exercise 6.4: A Simple Generator

> Source: Practical Python Programming, `06_Generators/02_Customizing_iteration.md`.

### Exercise 6.4: A Simple Generator

If you ever find yourself wanting to customize iteration, you should
always think generator functions.  They're easy to write---make
a function that carries out the desired iteration logic and use `yield`
to emit values.

For example, try this generator that searches a file for lines containing
a matching substring:

```python
>>> def filematch(filename, substr):
        with open(filename, 'r') as f:
            for line in f:
                if substr in line:
                    yield line

>>> for line in open('Data/portfolio.csv'):
        print(line, end='')

name,shares,price
"AA",100,32.20
"IBM",50,91.10
"CAT",150,83.44
"MSFT",200,51.23
"GE",95,40.37
"MSFT",50,65.10
"IBM",100,70.44
>>> for line in filematch('Data/portfolio.csv', 'IBM'):
        print(line, end='')

"IBM",50,91.10
"IBM",100,70.44
>>>
```

This is kind of interesting--the idea that you can hide a bunch of
custom processing in a function and use it to feed a for-loop.
The next example looks at a more unusual case.

## 关联来源

- [[summaries/02_Customizing_iteration]]