{"nbformat":4,"nbformat_minor":0,"metadata":{"kernelspec":{"display_name":"Python 3","language":"python","name":"python3"},"language_info":{"codemirror_mode":{"name":"ipython","version":3},"file_extension":".py","mimetype":"text/x-python","name":"python","nbconvert_exporter":"python","pygments_lexer":"ipython3","version":"3.7.3"},"colab":{"name":"03.d2.03.user-defined-functions.ipynb","provenance":[],"collapsed_sections":[]}},"cells":[{"cell_type":"markdown","metadata":{"id":"erisISfq75qt","colab_type":"text"},"source":["# [Functions](https://www.learnpython.org/en/Functions)\n","\n","**Rule of thumb:** if you need to perform a similar process multiple times then we should highly consider creating a function definition.\n","\n","A user defined function can be run multiple times whenever needed. These user defined functions can accept unique input each time, but the same operations defined in the user defined function body will be performed when the function is invoked. \n","\n","The output of the user defined functions are derived by the input of the function.\n","\n","The power of user defined functions come when using them within loops. "]},{"cell_type":"markdown","metadata":{"id":"zVJzG3jr75qx","colab_type":"text"},"source":["
"]},{"cell_type":"markdown","metadata":{"id":"H5o6uI7475qy","colab_type":"text"},"source":["

"]},{"cell_type":"markdown","metadata":{"id":"x9ujeHMy75qz","colab_type":"text"},"source":["***\n","
\n","
"]},{"cell_type":"markdown","metadata":{"id":"NwVstrEC75qz","colab_type":"text"},"source":["## 1. Functions WITHOUT Parameters/Arguments"]},{"cell_type":"markdown","metadata":{"id":"CjV9O2RT75q0","colab_type":"text"},"source":["#### Define a basic function."]},{"cell_type":"markdown","metadata":{"collapsed":true,"id":"rccKIsxS75q1","colab_type":"text"},"source":["```python\n","def my_first_function():\n"," print('Hello world!')\n","```"]},{"cell_type":"code","metadata":{"id":"sKVBj8rj75q2","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"VgwtKuaL75q5","colab_type":"text"},"source":["#### Check it's type"]},{"cell_type":"markdown","metadata":{"id":"0Xc915y275q6","colab_type":"text"},"source":["```python\n","print('type:', my_first_function)\n","```"]},{"cell_type":"code","metadata":{"id":"GAtAYq4-75q7","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"Tl5rhYk075q-","colab_type":"text"},"source":["#### Invoke the function with `()`.\n","Invoking a function means run the function, in other words, call the function."]},{"cell_type":"markdown","metadata":{"id":"098Ggsia75q_","colab_type":"text"},"source":["```python\n","my_first_function()\n","```"]},{"cell_type":"code","metadata":{"id":"LDsbDLXX75rA","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"B1iQoAfi75rD","colab_type":"text"},"source":["***\n","
\n","
\n","
"]},{"cell_type":"markdown","metadata":{"id":"g8kYBNI_75rF","colab_type":"text"},"source":["## 2. Functions WITH Parameters/Arguments\n","\n","It's important to note the difference of `parameters` and `arguments`. \n","\n","- `Parameter` is variable in the declaration of function \n","\n","- `Argument` is the actual value of this variable that gets passed to function\n","\n","A `parameter` is a variable in a function definition. When a function is called, the `arguments` are the data you pass into the function's parameters. "]},{"cell_type":"markdown","metadata":{"id":"WJMEaxAL75rG","colab_type":"text"},"source":["

"]},{"cell_type":"markdown","metadata":{"id":"fXfZKInb75rG","colab_type":"text"},"source":["#### Define a Function w/ parameters \"first\" and \"last\""]},{"cell_type":"markdown","metadata":{"collapsed":true,"id":"DPBrPEec75rH","colab_type":"text"},"source":["```python\n","def secret_agent_greeting(first, last):\n"," print('Call me', last + \",\", first, last + \".\")\n","```"]},{"cell_type":"code","metadata":{"id":"fpXfOgHf75rI","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"IVDC0Dqs75rM","colab_type":"text"},"source":["#### Call the function by passing in `arguments` in the same order as `parameters`\n","```python\n","secret_agent_greeting('James', \"Bond\")\n","```"]},{"cell_type":"code","metadata":{"id":"ozI4UQ1W75rN","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"OQlWHl0I75rS","colab_type":"text"},"source":["#### Check it's type"]},{"cell_type":"markdown","metadata":{"id":"Fv44IGv_75rU","colab_type":"text"},"source":["```python\n","print('type:', my_first_function)\n","```"]},{"cell_type":"code","metadata":{"id":"sX3i-YVF75rV","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"6rSzZc0m75rZ","colab_type":"text"},"source":["#### Call function with `()` and passing in arguments. "]},{"cell_type":"markdown","metadata":{"collapsed":true,"id":"TSFFOdFb75ra","colab_type":"text"},"source":["```python\n","secret_agent_greeting('James','Bond')\n","secret_agent_greeting('John', 'Doe')\n","\n","# Try your own\n","secret_agent_greeting(___, ___)\n","```"]},{"cell_type":"code","metadata":{"id":"Nyt5OCKR75rb","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"Pd-T38Pu75re","colab_type":"text"},"source":["***\n","
\n","
\n","
"]},{"cell_type":"markdown","metadata":{"id":"oeFV67X275rh","colab_type":"text"},"source":["## 3. The `return` Statement.\n","\n","In the previous user defined functions we only printed values to screen.\n","\n","One thing we might want to do is have a user defined function return a value from the operations performed within the function body. The reason we might want to return a value from a function would be to use that value in a later point of the program. \n","\n","With the previous user defined functions we would not be able to store print statements to a variable this way. \n","\n","Let's take a look at how we can change this using the keyword `return` in the function body.\n","\n","\n"]},{"cell_type":"markdown","metadata":{"id":"REiftw5J75rj","colab_type":"text"},"source":["#### Define a Function with a return value"]},{"cell_type":"markdown","metadata":{"collapsed":true,"id":"zyx4rLTU75rn","colab_type":"text"},"source":["```python\n","def strip_and_lowercase(original):\n"," modified = original.strip().lower()\n"," return modified\n","```"]},{"cell_type":"code","metadata":{"id":"24pX8jNs75ro","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"nl78lCkL75rs","colab_type":"text"},"source":["#### We'll use `ugly_string` as the `argument` for the `strip_and_lowercase` function. "]},{"cell_type":"markdown","metadata":{"collapsed":true,"id":"Gv50ADYt75rt","colab_type":"text"},"source":["```python\n","ugly_string = ' MixED CaSe '\n","```"]},{"cell_type":"code","metadata":{"id":"zQv1imWk75ru","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"7bh9TN4A75ry","colab_type":"text"},"source":["#### The strip_and_lowercase function \"returns\" a value, \n","> this means that we can store that value in a variable, in this case `pretty`."]},{"cell_type":"markdown","metadata":{"collapsed":true,"id":"doMO8KU475r0","colab_type":"text"},"source":["```python\n","pretty_string = strip_and_lowercase(ugly_string)\n","```"]},{"cell_type":"code","metadata":{"id":"xTnOCNAl75r1","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"1MPCEWuo75r4","colab_type":"text"},"source":["#### Print out the result"]},{"cell_type":"markdown","metadata":{"id":"LlIebQx_75r5","colab_type":"text"},"source":["```python \n","print('original:', ugly_string)\n","print('prettiffied:', pretty_string)\n","```"]},{"cell_type":"code","metadata":{"id":"hTcC49Uy75r6","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"MDkcV3I675r-","colab_type":"text"},"source":["***\n","
\n","

-----------Functions Exercises (1)-------------

\n","
"]},{"cell_type":"markdown","metadata":{"id":"oflVNd4E75r_","colab_type":"text"},"source":["## 4. \"Real-World\" Example\n","\n","In the next section I show an application of how we would use functions and for loops together to \"clean\" a collection of text."]},{"cell_type":"markdown","metadata":{"id":"dlmw5Rkf75sB","colab_type":"text"},"source":["

\n","\n","```python\n","messy_strings = [\n"," \"SallY\",\n"," \"Sally\",\n"," \" SALLY \",\n"," \" saLLY \",\n"," \" sALlY \",\n"," \" saLLy \",\n"," \" SAlly \",\n"," \" SALly \",\n"," \" sAlLy \",\n"," \"salLy \",\n"," \" sAllY \",\n"," \" SaLlY \",\n"," \" SAllY \",\n"," \" sALlY \",\n"," \" SaLlY \",\n"," \" SAlly \",\n"," \"SALLY \",\n"," \" saLLY \",\n"," \" sALlY \",\n"," \" saLLy \",\n"," \" SAlly \",\n"," \" SALly \",\n"," \"sAlLy \",\n"," \" salLy \",\n"," \" sAllY \",\n"," \" SaLlY \",\n"," \" SAllY \",\n"," \" sALlY \"\n","]\n","```\n","\n","

"]},{"cell_type":"code","metadata":{"id":"_FgP7ZFy75sC","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"3Tqjz4aQ75sH","colab_type":"text"},"source":["
"]},{"cell_type":"markdown","metadata":{"id":"hohtFnjG75sI","colab_type":"text"},"source":["### Function Calls within a `for loop`\n","\n","This is cool for just looking at what the function would do to the collection of text, but if we want to save the resulting data, we need to `append` each cleaned string to a `list` that we initialize `outside` of the `for` `loop`. See the next block.\n","\n","

\n","\n","```python\n","for sally in messy_strings:\n"," print(strip_and_lowercase(sally)) # use func on each \"sally\"\n","```\n","\n","

"]},{"cell_type":"code","metadata":{"id":"5g4Upt4e75sJ","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"WMFcrtPx75sL","colab_type":"text"},"source":["
"]},{"cell_type":"markdown","metadata":{"id":"JC56hEYu75sL","colab_type":"text"},"source":["### Function Calls to build a `list` with a `for loop`\n","\n","**Some things to note in this example:**\n","\n","1) We make an Empty list `clean_strings`, **outside** of the `for` `loop`.\n","\n","2) We save the `return` value of `strip_and_lowercase`, called on `sally_messy` —to variable `sally_clean`.\n","\n","3) We append each `sally_clean` to the end of `clean_strings` list.\n","\n","4) The `clean_strings` list will grow as we iterate through `mixed_strings`.\n","\n","\n","

\n","\n","```python\n","clean_strings = [] # new empty list\n","for sally_messy in messy_strings:\n"," sally_clean = strip_and_lowercase(sally_messy) # use func on each \"sally\"\n"," clean_strings.append(sally_clean) # Add each cleaned sally, one at a time to end of clean_strings\n","```\n","\n","

"]},{"cell_type":"code","metadata":{"id":"xgy2x77K75sM","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"eVeTWob275sO","colab_type":"text"},"source":["
"]},{"cell_type":"markdown","metadata":{"id":"tMkmvT3v75sO","colab_type":"text"},"source":["#### To check our work! `print()` both `messy_strings` and `clean_strings` lists. **Do they look different?** \n","\n","\n","

\n","\n","```python\n","print(\"Messy:\")\n","print(messy_strings)\n","print()\n","print(\"Cleaned:\")\n","print(clean_strings)\n","```\n","\n","

"]},{"cell_type":"code","metadata":{"id":"khl0rDE575sP","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"c0TOaxTy75sR","colab_type":"text"},"source":["***\n","
\n","
\n","
"]},{"cell_type":"markdown","metadata":{"id":"lgqFVBFD75sT","colab_type":"text"},"source":["## 5. Keyword parameters/arguments\n","\n","When we call a function with some values, these values get assigned to the arguments according to their position.\n","\n","Python allows functions to be called using keyword arguments. When we call functions in this way, the order (position) of the arguments can be changed.\n","\n","[Keyword arguments resource](https://www.programiz.com/python-programming/function-argument#key)"]},{"cell_type":"markdown","metadata":{"id":"Uqr5Ztzb75sW","colab_type":"text"},"source":["### Define function WITH Named Parameters."]},{"cell_type":"markdown","metadata":{"id":"d1rZJzmM75sX","colab_type":"text"},"source":["```python\n","def my_fancy_calculation(first, second, third):\n"," return first + second - third \n","```"]},{"cell_type":"code","metadata":{"id":"daw-VRNM75sY","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"zlrYB2uJ75sb","colab_type":"text"},"source":["### Invoke the function without named `arguments` "]},{"cell_type":"markdown","metadata":{"id":"0vBpGcSb75sc","colab_type":"text"},"source":["```python\n","# Invoking function without named arguments\n","print(my_fancy_calculation(3, 1, 2))\n","```"]},{"cell_type":"code","metadata":{"id":"sY0lt54AG3nm","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"b88G5sZo75sc","colab_type":"text"},"source":["### Invoke the function with named `arguments`\n","\n","```python\n","# Invoking function with named arguments\n","print(my_fancy_calculation(first = 3, second = 1, third = 2))\n","```"]},{"cell_type":"code","metadata":{"id":"GdgR7-ZjG4-x","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"fGO6sHzp75se","colab_type":"text"},"source":["### With keyword arguments you can mix the order"]},{"cell_type":"markdown","metadata":{"id":"h7lhPYBS75sg","colab_type":"text"},"source":["```python \n","print(my_fancy_calculation(third=1, first=3, second=2))\n","```"]},{"cell_type":"code","metadata":{"id":"rtcqVg2c75sh","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"VhOsUdK275sl","colab_type":"text"},"source":["### You can mix NON-keyword arguments AND keyword arguments. \n","**Not recommend** but you have to place any non-keyword arguments first."]},{"cell_type":"markdown","metadata":{"id":"Mn0GnQnu75sm","colab_type":"text"},"source":["```python\n","print(my_fancy_calculation(3, third=1, second=2))\n","```"]},{"cell_type":"code","metadata":{"id":"jyZzSeGH75sm","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"fqxJhFEB75sp","colab_type":"text"},"source":["***\n","
"]},{"cell_type":"markdown","metadata":{"id":"QwkIvgLE75sq","colab_type":"text"},"source":["## 6. Default user defined function arguments"]},{"cell_type":"markdown","metadata":{"collapsed":true,"id":"bS8QJ1i575sq","colab_type":"text"},"source":["Setting one of the `parameter`s in the `user defined function definition` equal to some value, say `job=None`, sets a default value for that parameter value. \n","
\n","\n","If the user does NOT provide an argument value for a parameter defined with a default value, the function \"knows\" to use the default value instead.\n","
\n","\n","In the example below, observe the function `create_person_info`. If we don't pass in a value to `job`, the function will know to use `None` as the value for `job`. \n","\n","```python \n","def create_person_info(name, age, job=None, salary=300):\n"," info = {\"name\": name, \"age\": age, \"salary\": salary}\n"," \n"," # Will be False if job=None\n"," if job: \n"," # Creates 'occupation' key if user provides an argument to 'job'\n"," info.update({'occupation': job})\n"," \n"," return info\n","```"]},{"cell_type":"code","metadata":{"id":"4bDay1oR75sr","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"FiGuK92U75st","colab_type":"text"},"source":["
"]},{"cell_type":"markdown","metadata":{"id":"ZE927MYr75su","colab_type":"text"},"source":["### Use default values for job and salary."]},{"cell_type":"markdown","metadata":{"id":"E__7SxQ375sv","colab_type":"text"},"source":["Here, we do not provide values to `job` or `salary`, we are relying on parameter order to create a person named `John Doe`, `82` years old, No occupation, with a `salary` of `300`.\n","\n","```python\n","person1 = create_person_info('John Doe', 82)\n","print(person1)\n","```"]},{"cell_type":"code","metadata":{"id":"cWGZit-W75sw","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"ILx_yvSO75sz","colab_type":"text"},"source":["
"]},{"cell_type":"markdown","metadata":{"id":"JjiNydOw75s0","colab_type":"text"},"source":["### Pass in values for each of the parameters."]},{"cell_type":"markdown","metadata":{"scrolled":true,"id":"J6xi5umt75s1","colab_type":"text"},"source":["Here, the parameters are all passed in, the order of the parameters is used.\n","\n","\n","```python\n","person2 = create_person_info('Lisa Doe', 22, 'hacker', 10000)\n","print(person2)\n","```"]},{"cell_type":"code","metadata":{"id":"Gmsrdvw775s2","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"rL9koOK-75s4","colab_type":"text"},"source":["***\n","
\n","
\n","
"]},{"cell_type":"markdown","metadata":{"id":"egAptU_r75s4","colab_type":"text"},"source":["## 7. The [`pass`](https://docs.python.org/3/reference/simple_stmts.html#the-pass-statement) statement\n","`pass` is a statement which does nothing when it's executed. It can be used as a placeholder to make the code syntatically correct while sketching the functions of your application. For example, the following is valid Python. "]},{"cell_type":"markdown","metadata":{"collapsed":true,"id":"Ezl9Y4CR75s5","colab_type":"text"},"source":["```python\n","def my_function(some_argument):\n"," pass\n","\n","def my_other_function():\n"," pass\n","```"]},{"cell_type":"code","metadata":{"id":"z8XoolRa75s5","colab_type":"code","colab":{}},"source":[""],"execution_count":0,"outputs":[]},{"cell_type":"markdown","metadata":{"id":"1mJ7Hp3C75s7","colab_type":"text"},"source":["***\n","
\n","

-----------Functions Exercises (2) (3)-------------

\n","
"]}]}

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