Python Loops

class: middle

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

---
class: middle

# Python Loops

---

# Agenda

1. [ ] [Lists](#lists)
2. [ ] [For Loops](#for-loop)
3. [ ] [While Loops](#while-loop)
4. [ ] [List Methods](#list-methods)
5. [ ] [Loop Practice](#loop-practice)

---
name: lists

# [Exercise 27](https://github.com/ts-cset/cset-160/blob/master/python/ex27.py)

- Lists! Our first data structure!
- Python Lists are very similar to JavaScript Arrays.
- Python has other data structures, too. We'll get to them later.
- If you're curious, look up the classical Computer Science definitions of <a href="https://en.wikipedia.org/wiki/List_(abstract_data_type)" target="_blank">Lists</a> and <a href="https://en.wikipedia.org/wiki/Array_data_type" target="_blank">Arrays</a> on Wikipedia.
    - Is there a difference?
    - Why do Python and JS use different names?

---
name: for-loops

# Exercise 27

- Look up the .eight[range] function and learn what it does.
- Could we remove the for loop on line 23 and just assign .eight[range(0,6)] to .eight[elements]?
- What other List methods can you use beside .eight[append()]?

---
name: while-loops

# [Exercise 28](https://github.com/ts-cset/cset-160/blob/master/python/ex28.py)

- Now we've seen both types of loops in Python.
- They're used the same as in JavaScript, so they should feel familiar.
- Is it usually better to use while loops or for loops?

.eleven[Remember: You can always stop your script from running by hitting CTRL-C]

---

# Exercise 28

- Wrap the while loop in a function you can call and convert the .eight[6] into an argument so this script can create lists of different sizes.
- Now add a second argument to the function that changes how every iteration increments on line 12.
- Finally, replace the while loop with a for loop and range. Do you need the line that increments .eight[i]?

---

# Accessing Items From Lists

Do you remember the difference between .eight[ordinal] and .eight[cardinal] numbers?

```python
my_list[0]
```

Just like JavaScript, you need to use an integer as the index.

---
name: list-methods

# Accessing Methods

```python
my_list.append('hello')
```

1. Python sees .eight[my_list], where did it come from?
2. Oh, it's a List. Lists have properties so the .eight[.] is okay.
3. Is .eight[append] in that group of properties? Yes, grab the value.
4. After append is a pair of parens. Is append a function? Yes, so call it.

---
class: middle, center

# .fourteen[Append was called with how many arguments?]

---

# Accessing Methods

Two. Think of it like this:

```python
append(my_list, 'hello')
```

.eight[my_list passes itself to it's methods]

---

# Try It

Open the REPL and type this:

```python
>>> class Thing(object):
...     def test(message):
...             print(message)
...
>>> a = Thing()
>>> a.test("hello")
```

---

# Accessing Methods

Remember this when you run into the following error:

```python
TypeError: some_method() takes 1 positional argument but 2 were given
```

---

# [Exercise 29](https://github.com/ts-cset/cset-160/blob/master/python/ex29.py)

- We can access items a little differently from JS
- Figure out what .eight[split] and .eight[join] do.
- The odd looking .eight[3:5] notation is a "slice" from a list. Look it up.
- Rewrite this script using a for loop. Which is easier? Which is simpler?

---
name: loop-practice

# More Practice With Loops

Let's recreate some of our JS functions into Python

1. [Looping A Triangle](https://eloquentjavascript.net/02_program_structure.html#i_umoXp9u0e7)
2. [FizzBuzz](https://eloquentjavascript.net/02_program_structure.html#i_rebKE3gdjV)
3. [Chessboard](https://eloquentjavascript.net/02_program_structure.html#i_swb9JBtSQQ)
4. [Minimum](https://eloquentjavascript.net/03_functions.html#i_XTmO7z7MPq)
5. [Recursion](https://eloquentjavascript.net/03_functions.html#i_jxl1p970Fy)
6. [Bean Counting](https://eloquentjavascript.net/03_functions.html#i_3rsiDgC2do)

---

# [Exercise 30](https://github.com/ts-cset/cset-160/blob/master/python/ex30.py)

- Let's add loops and functions to our game script
- On line 11, it says .eight[if "0" in choice], what does that do?
- This isn't the best way to look for number input. Change it to make it better.
- Look up what .eight[exit], .eight[break], and .eight[continue] do.