update readme

Author: JeffKatzy

README.md

@@ -1,322 +1,99 @@
 
-# For loops
+# Functions lab
 
-### Learning Objectives
+As we know, we can use functions to give a name to sequences of our code, to make it more expressive.  We can also use functions to allow us to reuse code.  In this lab we will get practice in using functions for these purposes.
 
-* Understand the components of a point in a graph, an $x$ value, and a $y$ value 
-* Understand how to plot a point on a graph, from a point's $x$ and $y$ value
-* Get a sense of how to use a graphing library, like Plotly, to answer questions about our data
+### Objectives
 
-### Picking up where we last left off
+* Practice declaring and returning values from function
+* Practice accessing variables outside of a function's scope, from inside of a function
 
-In the last lesson, we plotted some of our travel data.
+### Writing our first functions
 
-
-```python
-import pandas
-file_name = './cities.xlsx'
-travel_df = pandas.read_excel(file_name)
-cities = travel_df.to_dict('records')
-```
-
-
-```python
-import plotly
-
-plotly.offline.init_notebook_mode(connected=True)
-
-x_values = [cities[0]['City'], cities[1]['City'], cities[2]['City']]
-y_values = [cities[0]['Population'], cities[1]['Population'], cities[2]['Population']]
-
-trace_first_three_pops = {'x': x_values, 'y': y_values, 'type': 'bar'}
-# plotly.offline.iplot([trace_first_three_pops])
-```
-
-
-<script>requirejs.config({paths: { 'plotly': ['https://cdn.plot.ly/plotly-latest.min']},});if(!window.Plotly) {{require(['plotly'],function(plotly) {window.Plotly=plotly;});}}</script>
-
-
-Let's take another look at our `x_values` variable. 
-
-
-```python
-x_values = [cities[0]['City'], cities[1]['City'], cities[2]['City']]
-```
-
-As you can see, we go one by one through the `cities` list, and for each element of the cities list, we retrieve the `City` attribute.  This procedure of going one by one, and doing the same thing can be automated with the `for` loop.
-
-### Learning Objectives
-
-### Introduction to the For Loop
-
-A `for` loop in Python, is good at going through elements of a list one by one.  Let's take an initial array.
-
-
-```python
-zero_to_three = [0, 1, 2, 3]
-```
-
-Now to print the elements of a list, we currently do the following: 
-
-
-```python
-print(zero_to_three[0])
-print(zero_to_three[1])
-print(zero_to_three[2])
-```
-
-    0
-    1
-    2
-
-
-So we increase the index by one each time, starting at the number zero and ending at the number 2.  A `for` loop is great at going through these elements in the list.  For example:
-
-
-```python
-for i in [0, 1, 2]:
-    print(i + 5)
-```
-
-    5
-    6
-    7
-
-
-So note that above, our expression prints three times: once for each element in our list.  The first time it starts with the number 0, for that is the first element in the array, and then it goes forward to the second element, and then the third.  So we can use the `for` loop to operate on the numbers zero through two, and the `i` represents a successive element in our list each time.
-
-Pay careful attention to the syntax.  Essentially, Python needs to know when the body of the loop begins and when it ends.  So we mark the beginning of the loop's body with a colon, `:`, and then indent each successive line of the loop.  (If you press enter after the colon, the indent will come automatically).  To end the body of the loop, we simply unindent. 
-
-
-```python
-for i in [0, 1, 2]:
-    print(i + 5)
-print(10)
-```
-
-    5
-    6
-    7
-    10
-
-
-Just like any other variable, we can call the `i` whatever we like.  
-
-
-```python
-for number in [0, 1, 2]:
-    print(number + 5)
-```
-
-    5
-    6
-    7
-
-
-We just have to make sure that whatever word we use after `for` is referenced in our loop later on.
-
-
-```python
-for number in [0, 1, 2]:
-    print(what + 5)
-```
-
-
-    ---------------------------------------------------------------------------
-
-    NameError                                 Traceback (most recent call last)
-
-    <ipython-input-23-ba9129ae8cfe> in <module>()
-          1 for number in [0, 1, 2]:
-    ----> 2     print(what + 5)
-    
-
-    NameError: name 'what' is not defined
-
-
-### Using list elements as indices
-
-In the above section we iterated through a list of successive numbers.  Now remember that to access elements of any lists, we use a number to do so.
+Imagine we work in a diner.  We have a list of `orders` which we assign below.  Write a function called `number_of_orders` that returns the current number of orders.
 
 
 ```python
-countries = ['Croatia', 'USA', 'Argentina']
+orders = ['turkey sandwich', 'eggs']
+def number_of_orders():
+    pass
 ```
 
 
 ```python
-countries[0]
+number_of_orders() # 2
 ```
 
-
-
-
-    'Croatia'
-
-
+Now write another function called `next_up` that returns the first order (the order with the lowest index), in the `orders` list.
 
 
 ```python
-countries[2]
+def next_up():
+    pass
 ```
 
 
-
-
-    'Argentina'
-
-
-
-So to iterate through the elements of `countries`, we can do the following:  
-
-
 ```python
-for i in [0, 1, 2]:
-    print(countries[i])
-```
-
-    Croatia
-    USA
-    Argentina
-
+orders = ['turkey sandwich', 'eggs']
+next_up() # 'turkey sandwich'
 
-So notice what happened there.  Just like previously, our loop variable, `i`, is a different element of the list each time.  Because these elements are also the increasing indices for our list of `countries`, we can use them to access and then operate on the elements of the `countries`.
-
-
-```python
-for i in [0, 1, 2]:
-    print(i)
-    print(countries[i])
+orders = ['beet salad', 'fennel']
+next_up() # 'beet salad'
 ```
 
-    0
-    Croatia
-    1
-    USA
-    2
-    Argentina
-
-
-Of course, this only works if the elements of the list match up with the size of our list.  So it would be nice to perform some calculation to ensure that this is the case.  Let's do it.
-
-We can use the `len` function to calculate the size of our list.
+Ok, now write a function called `healthy_order` that returns the string `'spinach salad'`.
 
 
 ```python
-len(countries)
+def healthy_order():
+    pass
 ```
 
 
-
-
-    3
-
-
-
-Then we can turn this length into a successive list of elements with the following:
-
-First, create a range object:
-
-
 ```python
-range(0, len(countries))
+healthy_order() # 'spinach salad'
 ```
 
-
-
-
-    range(0, 3)
-
-
-
-And then convert this into a list:
+Now let's declare an array called `orders`.  Change the function `healthy_order` so that it continues to return the string `'spinach salad'`, but also adds the string `'spinach salad'` to the end of the list of orders.
 
 
 ```python
-list(range(0, len(countries)))
+orders = ['turkey sandwich', 'eggs']
+healthy_order()
+orders[-1] # 'spinach salad'
 ```
 
 
 
 
-    [0, 1, 2]
+    'eggs'
 
 
 
-Note that the range object is marking the starting and ending point, and excluding the end.  So this works perfectly:
+Now let's write another function iterates through the list of `orders` and capitalizes the first letter of each word in the order.  It should return a list of capitalized orders.
 
 
 ```python
-for i in list(range(0, len(countries))):
-    print(countries[i])
+orders = ['spinach salad', 'turkey sandwich']
+def capitalize_orders():
+    pass
 ```
 
-    Croatia
-    USA
-    Argentina
-
-
-And as we add or subtract countries, we will still be iterating through our list elements.
-
 
 ```python
-countries = ['Croatia', 'USA', 'Argentina']
-countries.append('Mexico')
-for i in list(range(0, len(countries))):
-    print(countries[i])
+capitalize_orders() # ['Spinach Salad', 'Turkey Sandwich']
 ```
 
-    Croatia
-    USA
-    Argentina
-    Mexico
-
-
-### Iterating through different datatypes
-
-So far our loop variable has always been an element of a list that is a number.  However, our block variable can represent any data type.  For example, let's have the block variable represent each of the countries directly:
+Now if someone adds, an upcapitalized order, we can simply call our function again to return a list of capitalized orders.
 
 
 ```python
-countries = ['Croatia', 'USA', 'Argentina']
-for i in countries:
-    print(i)
+orders = ['spinach salad', 'turkey sandwich']
+capitalize_orders() # ['Spinach Salad', 'Turkey Sandwich']
+orders.append('eggs')
+capitalize_orders() # ['Spinach Salad', 'Turkey Sandwich', 'Eggs']
 ```
 
-    Croatia
-    USA
-    Argentina
-
-
-So now `i` points to each element of the `countries` list.  We previously used `i` as `i` was equal to an index of a list.  However, here our block variable will equal an individual country.  Might as well be expressive:
-
-
-```python
-for country in countries:
-    print(country)
-```
-
-    Croatia
-    USA
-    Argentina
-
-
-This is a standard pattern.  The variable name pointing to a list is plural, and to refer to a singular element as a loop variable, use the singular version.  So if we were printing out a list of friends name, we would write it as the following:
-
-
-```python
-friends = ['Bob', 'Sally', 'Fred']
-for friend in friends:
-    print(friend)
-```
-
-    Bob
-    Sally
-    Fred
-
-
-And there we are printing out a list of friends.
-
 ### Summary
 
-In this section, we saw how we can use loops to iterate through various elements.  This is a very powerful 
+Great job.  Through this lab you were able to get practice both writing and returning values from functions.  You also practiced accessing variables not local to the function, but in the global scope.