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David Beazley
2020-05-28 10:22:32 -05:00
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Notes/03_Program_organization/06_Design_discussion.md
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[Contents](../Contents) \| [Previous (3.5 Main module)](05_Main_module) \| [Next (4 Classes)](../04_Classes_objects/00_Overview)
# 3.6 Design Discussion
In this section we consider some design decisions made in code so far.
In this section we reconsider a design decision made earlier.
### Filenames versus Iterables
@@ -35,15 +37,17 @@ with open('file.csv') as f:
* Which of these functions do you prefer? Why?
* Which of these functions is more flexible?
### Deep Idea: "Duck Typing"
[Duck Typing](https://en.wikipedia.org/wiki/Duck_typing) is a computer programming concept to determine whether an object can be used for a particular purpose. It is an application of the [duck test](https://en.wikipedia.org/wiki/Duck_test).
[Duck Typing](https://en.wikipedia.org/wiki/Duck_typing) is a computer
programming concept to determine whether an object can be used for a
particular purpose. It is an application of the [duck
test](https://en.wikipedia.org/wiki/Duck_test).
> If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.
In our previous example that reads the lines, our `read_data` expects
any iterable object. Not just the lines of a file.
In the second version of `read_data()` above, the function expects any
iterable object. Not just the lines of a file.
```python
def read_data(lines):
@@ -76,7 +80,7 @@ data = read_data(lines)
There is considerable flexibility with this design.
*Question: Shall we embrace or fight this flexibility?*
*Question: Should we embrace or fight this flexibility?*
### Library Design Best Practices
@@ -87,10 +91,10 @@ Don't restrict your options. With great flexibility comes great power.
### Exercise 3.17: From filenames to file-like objects
In this section, you worked on a file `fileparse.py` that contained a
You've now created a file `fileparse.py` that contained a
function `parse_csv()`. The function worked like this:
```pycon
```python
>>> import fileparse
>>> portfolio = fileparse.parse_csv('Data/portfolio.csv', types=[str,int,float])
>>>
@@ -103,8 +107,8 @@ with any file-like/iterable object. For example:
```
>>> import fileparse
>>> import gzip
>>> with gzip.open('Data/portfolio.csv.gz', 'rt') as f:
... port = fileparse.parse_csv(f, types=[str,int,float])
>>> with gzip.open('Data/portfolio.csv.gz', 'rt') as file:
... port = fileparse.parse_csv(file, types=[str,int,float])
...
>>> lines = ['name,shares,price', 'AA,34.23,100', 'IBM,50,91.1', 'HPE,75,45.1']
>>> port = fileparse.parse_csv(lines, types=[str,int,float])
@@ -120,8 +124,7 @@ In this new code, what happens if you pass a filename as before?
>>>
```
With flexibility comes power and with power comes responsibility. Sometimes you'll
need to be careful.
Yes, you'll need to be careful. Could you add a safety check to avoid this?
### Exercise 3.18: Fixing existing functions