Lecture 5

class: title-slide, left, bottom

# Lecture 5
----
## **DANL 100: Programming for Data Analytics**
### Byeong-Hak Choe
### September 13, 2022

---
# Announcement

### Accounting Expo

- Are you interested in learning about Accounting, Consulting, Audit or Tax?
  - Stop in for pizza and meet 20+ Firms (alumni and employers) from the Big 4, National Players and Regional firms!

- When? September 15th, 5:00 PM-7:00 PM

- Where? Ballroom

- Dress code? Business Casual

- Practice, prep or questions? In-person drop-ins!
  - South 110 (or 112) on September 13, 9:00 AM-Noon
  - South 110 (or 112) on September 14, 9:00 AM-4:00 PM
  
  
---
# Announcement

### How to use Canvas?

- Here is a brief introductory video of using Canvas: 
  - [Link](https://vimeo.com/74677642)

---
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# Workflow
<html><div style='float:left'></div><hr color='#EB811B' size=1px width=796px></html>

---
# Workflow
### Shortcuts 
- **F9** runs a current line (where the blinking cursor bar is) or selected lines.

- **Home/End** moves the blinking cursor bar to the beginning/end of the line.
 - **Fn + ** <svg aria-hidden="true" role="img" viewBox="0 0 448 512" style="height:1em;width:0.88em;vertical-align:-0.125em;margin-left:auto;margin-right:auto;font-size:inherit;fill:currentColor;overflow:visible;position:relative;"><path d="M447.1 256C447.1 273.7 433.7 288 416 288H109.3l105.4 105.4c12.5 12.5 12.5 32.75 0 45.25C208.4 444.9 200.2 448 192 448s-16.38-3.125-22.62-9.375l-160-160c-12.5-12.5-12.5-32.75 0-45.25l160-160c12.5-12.5 32.75-12.5 45.25 0s12.5 32.75 0 45.25L109.3 224H416C433.7 224 447.1 238.3 447.1 256z"/></svg> / <svg aria-hidden="true" role="img" viewBox="0 0 448 512" style="height:1em;width:0.88em;vertical-align:-0.125em;margin-left:auto;margin-right:auto;font-size:inherit;fill:currentColor;overflow:visible;position:relative;"><path d="M438.6 278.6l-160 160C272.4 444.9 264.2 448 256 448s-16.38-3.125-22.62-9.375c-12.5-12.5-12.5-32.75 0-45.25L338.8 288H32C14.33 288 .0016 273.7 .0016 256S14.33 224 32 224h306.8l-105.4-105.4c-12.5-12.5-12.5-32.75 0-45.25s32.75-12.5 45.25 0l160 160C451.1 245.9 451.1 266.1 438.6 278.6z"/></svg> works too.

.pull-left[
### Mac 
- **command + N** opens a new script.
- **command + 1** is the shortcut for #.
- **command + 4** is the shortcut for block comment.
]

.pull-right[
### Windows 
- **Ctrl + N** opens a new script.
- **Ctrl + 1** is the shortcut for #.
- **Ctrl + 4** is the shortcut for block comment.
]

---
# Workflow
### More Shortcuts

- **Ctrl** (**command** for Mac Users) **+ Z** undoes the previous action.
- **Ctrl** (**command** for Mac Users) **+ Shift + Z** redoes when undo is executed.

- **Ctrl** (**command** for Mac Users) **+ F** is useful when finding a phrase in the script.
- **Ctrl** (**command** for Mac Users) **+ R** is useful when replacing a specific phrase with something in the script.

- **Ctrl** (**command** for Mac Users) **+ D** deletes a current line.

---
# Workflow
### Code and comment style 
- The two main principles for coding and managing data are:
 - Make things easier for your future self.
 - Don't trust your future self.

- The `#` mark is Spyder's comment character.
  - The `#` character has many names: `hash`, `sharp`, `pound`, or `octothorpe`.
  - `#` indicates that the rest of the line is to be ignored.
  - Write comments before the line that you want the comment to apply to.

- Consider using block commenting for separating code sections.
  - `#%%` defines a coding block in Spyder.

---
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# Data: Types, Values, Variables, and Names
<html><div style='float:left'></div><hr color='#EB811B' size=1px width=796px></html>

---
# Data: Types, Values, Variables, and Names
### Python’s basic data types

- **Type** contains the Python name of that type. 
- **Mutable?** indicates whether the value can be changed after creation.

---
# Data: Types, Values, Variables, and Names
### Mutability

- The type determines whether the data value contained by the box can be changed (mutable) or is constant (immutable).

- A mutable object is like a box with a lid: not only can we see the value inside, we can also change it; 
  - However, we can’t change the type of an object.

.pull-left[

```python
a = (1, 2, 3)     # tuple
a[0]
a[0] = 5
a
```
]
.pull-right[

```python
b = [1, 2, 3]     # list
b[0]
b[0] = 5
b
```
]

---
# Data: Types, Values, Variables, and Names
### Assignment

- In Python, we use `=` to assign a value to a variable.

```python
# Here we assign the integer value 5 to the variable x.
x = 5

# Now we can use the variable x in the next line.
y = x + 12  
y
```

- In math, `=` means *equality* of both sides.
- In programs, `=` means **assignment**: *assign the value on the right side to the variable on the left side*.

---
# Data: Types, Values, Variables, and Names
### Variables Are Names, Not Places

- In Python, *variables* are just names.

<div class="figure" style="text-align: center">
<img src="../lec_figs/int-py-fig2-3.png" alt="Names point to objects (variable `a` points to an integer object with value `7`)" width="29%" />
Names point to objects (variable `a` points to an integer object with value `7`)
</div>

---
# Data: Types, Values, Variables, and Names
### Copying

- Assignment does not copy a value; 
  - It just attaches a name to the object that contains the data.

- What value is *assigned* to variable `y` at the end of the following code?

```python
# Here we assign the integer value 5 to the variable x.
x = 5

# Now we can use the variable x in the next line.
y = x + 12  
y

x = 8
```

---
# Data: Types, Values, Variables, and Names
### Copying

- Assigning an existing variable `a` to a new variable named `b`
just makes `b` point to the same object that `a` does.

<div class="figure" style="text-align: center">
<img src="../lec_figs/int-py-fig2-4.png" alt="Copying a name (now variable `b` also points to the same integer object)" width="29%" />
Copying a name (now variable `b` also points to the same integer object)
</div>

---
# Data: Types, Values, Variables, and Names
### Copying

- A **list** is a *mutable* array of values.

- In the code below, `a` and `b` each points to a list with three integer members:

```python
a = [2, 4, 6]
b = a
a[1] = 0
```

- List members (`a[0]`, `a[1]`, and `a[2]`) are themselves like names, pointing to integer objects with the values 2, 4, and 6.

- If both names point to a mutable object, we can change the object’s value via either name, and we’ll see the changed value when we use either name.

---
# Data: Types, Values, Variables, and Names
### Choose Good Variable Names

- It’s surprising how important it is to choose good names for your variables.

- In many of the code examples so far, I’ve been using throwaway names like `a` and `x`.

- In real programs, you’ll have many more variables to keep track of at once, and you’ll need to balance *brevity* and *clarity*.

- For example, it’s faster to type `num_loons` rather than `number_of_loons` or `blueberry_inventory`, but it’s more explanatory than `n`.

---
# Data: Types, Values, Variables, and Names
### Class Exercises 
1. Assign the integer value 33 to the variable `queen`, and print it.

2. What type is the value `3`?

3. What type is the value `3.0`?

4. What type is the expression `8 + 3.0`?

5. Modify the following line of code, so that a variable of string type data (`<class 'str'>`) is created.

```python
var_created = 1.5
print( "The data type of var_created is: ", type(var_created) )
```

---
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# Numbers
<html><div style='float:left'></div><hr color='#EB811B' size=1px width=796px></html>

---
# Numbers

- Let's look at the following Python’s simplest built-in data types in detail:

- **Booleans** (which have the value `True` or `False`)
  
  - **Integers** (whole numbers such as `10` and `28`)
  
  - **Floats** (numbers with decimal points such as `3.141592`, or sometimes exponents like `1.0e8`, which means one times ten to the eighth power, or `100000000.0`)

---
# Numbers
### Booleans

- The only values for the boolean data type are `True` and `False`.

- The special Python function `bool()` can convert any Python data
type to a boolean.
  - The `bool()` function takes any value as its argument and returns the boolean equivalent.
  
.pull-left[

```python
bool(True)
bool(1)
bool(4)
bool(-4)
```
]

.pull-right[

```python
bool(False)
bool(0)
bool(0.0)
```
]

---
# Numbers
### Integers

- Any sequence of digits in Python represents *a literal integer*:

.pull-left[
- We can’t have an initial 0 followed by a digit between 1 and 9:

```python
0
01
```
]

.pull-right[
- We can’t have any commas as a digit separator in the integer.
- We can use the underscore (`_`) character as a digit separator

```python
1,000,000   # We get a tuple!
billion = 1_000_000_000
billion
3_2_1
```

]

---
# Numbers
### Integer Operations

.pull-left[
- Python can be a simple calculator.

- Here is a table of the math operators:

]
.pull-right[
- Dividing by zero with either kind of division causes a Python exception

```python
12 + 8
12 - 8
13 * 1.2
2 + 3 * 4
2 ** 3
2 / 0
2 // 0
```
]

---
# Numbers
### Integers and Variables

- In Python, the expression on the right side of the `=` is calculated first, and then assigned to the variable on the left side.

.pull-left[
- Subtract `2` from `a`.
- Assign the result of that subtraction to a temporary variable, `tmp`.
- Assign the value of the temporary variable to `a`.

]
.pull-right[

```python
a = 72
tmp = a - 2
a = tmp
```
]

---
# Numbers
### Integers and Variables

- We can combine the arithmetic operators with assignment by putting the operator before the `=`.

.pull-left[

```python
a = 72
a -= 2   # This is like a = a - 2
```

]

.pull-right[

```python
b = 62
b += 2    # This is like b = b + 2
```
]

.pull-left[

```python
c = 72
c *= 2   # This is like c = c * 2
```

]

.pull-right[

```python
d = 62
d /= 2    # This is like d = d / 2
```

]

---
# Numbers
### Type Conversions

- To change other Python data types to an integer, use the `int()` function.
  - `int()` keeps the whole number and discard any fractional part.

- `True` and `False` are converted to integer values `1` and `0`.

.pull-left[

```python
int(True)
int(False)
```

]

.pull-right[

```python
bool(1)
bool(0)
```
]

.pull-left[

```python
int(72.3)
int(1.0e4)
```

]

.pull-right[

```python
bool(1.0)
bool(0.0)
```

]

---
# Numbers
### Floats

- Integers are whole numbers, but floating-point numbers (called **floats** in Python) have decimal points:

.pull-left[

```python
4.
4.0
04.0
```

]

.pull-right[

```python
4e0
4e1
4.0e1
4.0 * (10 ** 1)
```
]

---
# Numbers
### Floats

- To convert other types to floats, we use the `float()` function.

.pull-left[

```python
float(True)
float(False)
```

]

.pull-right[

```python
float(88)
float('89')
```
]

---
# Workflow
### Continue Lines with `\`

- Programs are more readable when lines are reasonably short. 
  - The recommended maximum line length is 80 characters.

- If you can’t say everything you want to say in that length, you can use the continuation character: `\` (backslash).

- Just put `\` at the end of a line, and Python will suddenly act as though you’re still on the same line.

---
# Workflow
### Continue Lines with `\`

.panelset[

.panel[.panel-name[With `\`]

```python
sum = 1 + \
      2 + \
      3 + \
      4
sum
```
]

.panel[.panel-name[Without `\`]

```python
sum = 1 + 
```
]

.panel[.panel-name[With `()`]
- If you’re in the middle of paired parentheses (or square or curly brackets), Python doesn’t squawk about line endings:

```python
sum = ( 1 +  
        2 +  
        3 +
        4 )
sum
```
]

]

---
# Numbers
### Class Exercises 
1. Multiply the number of seconds in a minute (`60`) by the number of minutes in an hour (also `60`) using Python.

2. Assign the result from the previous task (seconds in an hour) to a variable called `seconds_per_hour`.

3. How many seconds are in a day? Use your `seconds_per_hour` variable.

4. Calculate seconds per day again, but this time save the result in a variable called `seconds_per_day`

5. Divide `seconds_per_day` by `seconds_per_hour`. Use floating-point (`/`) division.

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# Choose with `if`
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