Intro to Back-End Programming

class: middle

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

---
class: middle

# Intro to Back-End Programming

---

# Agenda

1. [ ] Client-Server Model
2. [ ] Overview of Languages
3. [ ] Stupid Tourism
4. [ ] Why Python?
5. [ ] Start Scripting!

---

# Client-Server Model

"Application structure that distributes work between service or resource providers, .eight[servers], and requesters or consumers, called .eight[clients]."

---
class: center

---

# Waiter-Chef Metaphor

- You are the end user.
- The waiter takes your order and requests it from the chef.
- The chef prepares your order.
- And the waiter delivers it.

---

# Interesting Notes

- You or the waiter don't need to know how to make the food.
- The waiter and chef need to speak the same language.
- There can be many waiters for one chef.
- You never interact with the chef.
- Both the waiter and the chef need similar ideas about how things can go wrong.

---

## Many Levels of .eight[Client]-.fourteen[Server]

1. You use a .eight[web browser] to log in to your online banking service.
2. The .eight[web browser] sends the credentials as a request to the .fourteen[web server] to be processed by the back-end application.
3. The .eight[application] checks those credentials by sending a request to the .fourteen[database server].
4. If the credentials are good, the .fourteen[aplication] responds with the requested resource.
5. The .eight[web browser] displays it.

---

# Common Servers

- Web (Apache, Nginx)
- Email
- Network Printing

---
class: middle, center

# .fourteen[Does your portfolio site follow the client-server model?]

---

# Overview of Programming Languages

- Specification vs. Implementation
- Compiled vs. Interpreted (vs. Transpiled)
- Low-level vs. High-level
- Domain Specific vs. General Purpose

---
class: middle, center

# .fourteen[Isn't this a Web Dev class?]

---

# Domain vs. General Purpose

- .eight[Front-End Web]: JavaScript
- .eight[Back-End Web]: JavaScript, PHP, Java, Ruby, Python
- .eight[Mobile Apps]: Objective-C, Swift, Java, C#
- .eight[Game Dev]: C++, C#
- .eight[Desktop Apps]: Java, C++, C#, Python
- .eight[Systems]: C, Rust, Go, Python
- .eight[Math/Stats]: R, Julia, Python
- .eight[AI]: Lisp, Java, Python

---
class: middle, center

# .eleven[Stupid Tourism]

---
class: middle

# Why Python?

- Interpreted, High-Level, General Purpose
- Emphasizes Readability
- Dynamic Types and Memory Management
- Supports Multiple Paradigms

---

# The Zen of Python

- Beautiful is better than ugly
- Explicit is better than implicit
- Simple is better than complex
- Complex is better than complicated
- Readability counts

[read more here](https://en.wikipedia.org/wiki/Zen_of_Python)

---

# Install Python3

```sh
$ brew install python3
$ python3 --version
```

# .eleven[python3 != python]

---

# Why Python 3?

- 3.0 was created 11 years ago
- Not backwards compatible...
- 2.7's end-of-life ~was 2015~ is 2020

---

# Start Scripting!

```sh
$ python3
Python 3.6.5 ...
>>> quit()
$
```

---

# Start Scripting!

- Make a new directory for our Python exercises
- Move into it
- Make a new file called .eight[ex01.py]
- Use whatever editor you want
- Make a new file for each of our exercises

---

# Exercise 01

```python
print("Hello World!")
print("I like printing things.")
print("This is fun!")
print('I just said "This is fun!"')
print("Don't you agree?")
```

---

# Exercise 01

```sh
$ python3 ex01.py
```

- Add another print statement. Can you print a number?
- Put a .eight[#] before one of the lines. What did it do?

---

# Exercise 01

- Strings are in double or single quotes: .eight[""] .eight['']
- Comments start with octothorpes: .eight[#]

```python
# Comments can be whole lines
print("or...")  # at the end of lines
```

---

# Exercise 02

```python
# Math!

print(25 + 30 / 6)
print(100 - 25 * 3 % 4)

print(3 + 2 + 1 - 5 + 4 % 2 - 1 / 4 + 6)

print("True or False?", 3 < 7)
print("Greater than or equal to?", 3 >= 7)
```

---

# Exercise 02

Mathematical operators: 
```python
+ - / * %
```
Comparison operators:
```python
< > <= =>
```

---

# Exercise 02

.eight[2] is an integer, .eight[2.0] is a floating point number. Rewrite using .eight[floating point] numbers.

Now rewrite the file line by line using the REPL.
```
$ python3
>>> 2 + 3
5
```

---

# Exercise 03

```python
cars = 100
space_in_a_car = 4.0
drivers = 30
passengers = 90
cars_not_driven = cars - drivers
cars_driven = drivers
carpool_capacity = cars_driven * space_in_a_car
average_passengers_per_car = passengers / cars_driven

print("There will be ", cars_not_driven, " empty cars")
print("We can transport ", carpool_capacity, " people today.")
print("We need to put about ", average_passengers_per_car, " in each car")
```

---

# Exercise 03

- Don't need a keyword to make a variable
- By convention, names use snake_case
- Print can handle multiple arguments
- By convention, put a space between operators

---

# Exercise 03

- Line 2 has a floating point number. Is it necessary?
- Try changing it.
 
---

# Exercise 04

```python
name = 'Zed Shaw'
age = 35
height = 74 # inches
weight = 180 # lbs
eye_color = 'blue'
hair_color = 'brown'

print(f"Let's talk about {name}")
print(f"He's {height} inches tall")
print(f"He's {weight} pounds heavy")
print(f"He's got {eye_color} eyes and {hair_color} hair")
```

---

# Exercise 04 (cont.)

```python
total = age + height + weight
print(f"If I add {age}, {height}, and {weight} I get {total}.")
```

---

# Exercise 04

These are called .eight[Format Strings]. You're telling python to format the string before you print it.

- Write some variables that convert the numbers to metric.
- Try to find some variable names that aren't allowed

---

# Exercise 05

```python
types_of_people = 10
x = f"There are {types_of_people} types of people."

binary = "binary"
do_not = "don't"
y = f"Those who know {binary} and those who {do_not}"

print(x)
print(y)

print(f"I said: {x}")
print(f"I also said: {y}")
```

---

# Exercise 05 (cont.)

```python
hilarious = False
joke_evaluation = "Isn't that joke funny? {}"

print(joke_evaluation.format(hilarious))

w = "This is the left side of..."
e = "a string with a right side."

print(w + e)
```

---

# Exercise 05

- .eight[.format()] is the other way to format strings
- .eight[f] is helpful for strings you're creating
- .eight[.format()] is helpful for strings that already exist

---

# Exercise 05

1. Switch computers with a friend.
2. Find a small way to break their code.
3. Switch them back.
4. Try to fix your code.

---

# Exercise 06

```python
print("Mary had a little lamb,")
print("Its fleece was white as {},".format('snow'))
print("And everywhere that Mary went,")
print("." * 10) # what???

a = 'C'
b = 'h'
c = 'e'
d = 'e'
e = 's'
f = 'e'
g = 'b'
h = 'u'
i = 'r'
j = 'g'
k = 'e'
l = 'r'

print(a + b + c + d + e + f, end=' ')
print(g + h + i + j + k + l)
```

---

# Exercise 06

- Try keeping a list of all the mistakes you make.
- Before starting a new exercise, look over the list and try not to make the same mistakes against.
- Also, try adding a comment above every line describing what it does.

Now, let's swap computers with someone else and break things again!!!

---

# Exercise 07

```python
formatter = "{} {} {} {}"

print(formatter.format(1, 2, 3, 4))
print(formatter.format('one', 'two', 'three', 'four'))
print(formatter.format(True, False, False, True))
print(formatter.format(formatter, formatter, formatter, formatter))
print(formatter.format(
  "Try your",
  "Own text here",
  "Maybe a poem",
  "Or song lyrics"
))
```

---

# Exercise 07

Someone explain what's happening here?

---

# Exercise 08

```python
days = "Mon Tue Wed Thu Fri Sat Sun"
months = "Jan\nFeb\nMar\nApr\nMay\nJune\nJuly"

print("Here are the days: ", days)
print("Here are the months: ", months)

print("""
There's something going on here.
With the three double-quotes.
We'll be able to type as much as we like.
""")
```

---

# Exercise 08

- Look up a list of Python's escape sequences.
- Try to print them!

---

# Exercise 09

```python
tabby_cat = "\tI'm tabbed in."
persian_cat = "I'm split\non two lines."
backslash_cat = "I'm \\ a \\ cat."

fat_cat = """
I'll do a list:
\t* cat food
\t* fishies
\t* catnip\n\t* grass
"""

print(tabby_cat)
print(persian_cat)
print(backslash_cat)
print(fat_cat)
```

---
class: middle, center

# The End!