Python Input

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# .eight[CSET 160:]
## .eight[Web Development II]

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# Python Input

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# Agenda

1. [ ] Review Yesterday's Exercises
2. [ ] User Input
3. [ ] Script Arguments
4. [ ] Handling Files

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# Review

- Printing
- Assign Variables
- Data Types
- Simple Math and Comparison
- String Formatting

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# Python Documentation

## [https://docs.python.org/3/](https://docs.python.org/3/)

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# Searching

## .fourteen[python3 THING]

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# [Exercise 10](https://github.com/ts-cset/cset-160/blob/master/python/ex10.py)

- Use the python documentation to find out what .eight[input()] does.
- Try writing another "form" like this. Can you ask for numbers and do math with them?
- If you read about .eight[input()], you might have seen that it can take an argument. Rewrite this exercise to only use three .eight[input]s and a final .eight[print] statement at the end.

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# Exercise 10

In your terminal, run this command:
```sh
$ pydoc input
```
You can get out of pydoc by typing .eight[q]. Try using pydoc for otherthings we've seen so far. Or, if you're feeling brave, try looking up .eight[open], .eight[file], .eight[os], or .eight[sys].

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# [Exercise 11](https://github.com/ts-cset/cset-160/blob/master/python/ex11.py)

- Don't run this yet.
- On line 3, we're .eight[importing] a .eight[module].
- On line 5, we're *unpacking* a variable into many variables. It's called .eight[multiple assignment].

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# Exercise 11

So far, we've been calling scripts like this:
```sh
$ python3 script.py
```
Where .eight[script.py] is an argument for the .eight[python3] command. Now, let's call our new script with arguments of its own:
```sh
$ python3 ex11.py one two three
```

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# Exercise 11

- Now that you know what this script is doing, rename your variables so they make sense.
- Try calling this script with your own arguments.
- What happens if you use too many? Or not enough?
- Think about why you would use arguments over inputs.

### Anytime you see .eleven[argv], make sure you're calling the script properly!

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# [Exercise 12](https://github.com/ts-cset/cset-160/blob/master/python/ex12.py)

- Don't forget to run this script with the right arguments.
- Look up the games *Zork* and *Adventure* and play them sometime.
- Try to change the prompt.
- Add another argument into this script.

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# [Exercise 13](https://github.com/ts-cset/cset-160/blob/master/python/ex13.py)

This exercise needs another file. Call it .eight[ex13_sample.txt] here is its contents:

```md
This is stuff I typed into a file.
It is really cool stuff.
Lots and lots of stuff in here...
```

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# Exercise 13

- .eleven[Working with files is an easy way to **erase your work** if you aren't careful]
- We don't want to *hard code* the filename, so we use .eight[argv] or .eight[input].
- Write comments above each line to figure out what is happening in this file.
- Try only using .eight[input] to run this script. What are the benefits to using one or the other?
- Try using .eight[open()] and .eight[read()] from the Python REPL. Does it work the same way?

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# Exercise 13

## .eleven[Important Note!]

Python is interacting with the filesystem and treating these files as *external* resources. It can't guarantee that the filesystem closed what it opened, so you should do it **explicitly**.

Add this to the end of your script:
```python
txt.close()
txt_again.close()
```

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# [Exercise 14](https://github.com/ts-cset/cset-160/blob/master/python/ex14.py)

- Let's make a basic file editor!
- Try running this script using a filename that doesn't exist. Does it break?
- There's too much repetition here. Rewrite the script to use a single .eight[target.write()] command instead of six.
- Figure out why we had to pass a .eight['w'] to open the file.

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# Exercise 14

You should know the following file functions:

- .eight[close]
- .eight[read]
- .eight[readline]
- .eight[truncate]
- .eight[write]
- .eight[seek(0)]

Also, look up all the file modes you can pass to .eight[open].

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# [Exercise 15](https://github.com/ts-cset/cset-160/blob/master/python/ex15.py)

- We're importing a new module, .eight[exists()], to get a Boolean value by checking the existence of a file.
- This script is kind of annoying. Try to remove some features to make it simpler.
- See how short you can make this file. Can you get it to one line?

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# More Practice

- If you can make a copy script, can you make a move script?
- What other file-related scripts can you make?
- Can you use the same file functions in the REPL?

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The End!