# Module 0.9.0 - Exception Handling

* handling errors \[exceptions] in python
  * prevents code from breaking

## 0.9.1 - Error Types

* in most programming languages, there are three main types of erros

1. Syntax Error - occurs when the syntax of a program is incorrect

```
# the "print" function is spelled incorrectly [pint]
pint("Hello, World")
>>> ERROR
```

2. Run-Time Error - occurs when invalid data is inputted during "runtime"
   * runtime, any time after a program starts running

```
# this program asks for integer input, the user inputs a string
int(input("What is your favorite number? : "))
>>> What is your favorite number? : tree
>>> ERROR
```

3. Logical Error - Program runs as normal but not as intended
   * typically the hardest to find

```
# the program is intended to print their name before their age
name = "bob"
age = "100"
print(f"Hello, my name is {age} and I am {name} years old")

>>> "Hello, my name is 100 and I am bob years old"
```

## 0.9.2 - Try & Except Statements

* permits the developer to *try* a code segment, *except* if it doesn't work, it will run a different code segment
* "try" statement, try code that may cause an exception
* "except" statement, if an exception occurs in the try block, it will stop running, and run a different segment of code

```
try:
	print(2/0)
	print("This will not print")
	
except:
	print("You can't divide by zero")
```

it is good practice to specify the exception the program is looking for

```
try:
	print(2/0)
	print("This will not print")
	
except ZeroDivisionError:
	print("You can't divide by zero")
```

you can specify multiple exceptions in the exception block

```
try:
	print(2/0)
	print("This will not print")
	
except ZeroDivisionError, TypeError:
	print("Error)
```

you can chain except statements to specify multiple exceptions

```
try:
	money = "10"
	# "money" is a string, the following will cause a type error
	print(money - 3)
	print("This will not print")
	
except ZeroDivisionError:
	print("You can't divide by zero")
	
except TypeError:
	print("You can't subtract an integer from a string")
```

## 0.9.3 - Raise

* "raise" statement, displays the error that occured in the "try" statement
* good for figuring out what error you are dealing with

```
try:
	print(2/0)
	print("This will not print")
	
except:
	print("Error")
	raise
```

"raise" can also be used to throw an exception into runtime

```
print("Hello World!")
raise ZeroDivisionError
print("Will not run")
```

you can add a description with raised errors

```
print("Hello World!")
raise ZeroDivisionError("incorrect value")
print("Will not run")
```

## 0.9.4 - Finally

* "finally" statement, runs code no matter what
* comes last when creating "try" and "except" statements

```
try:
   print(2/0)
   print("This will not print")
   
except ZeroDivisionError:
   print("You can't divide by zero")
   
finally:
   print("This will print no matter what")
```

## 0.9.5 - Assertion

* "assert" statement, uses boolean operators to test an expression
  * if true, the code will run as normal
  * if false, the code will raise an "AssertionError" exception
  * good for testing

```
account = 100

# checks to see if account has the proper value
assert account == 50 
>>> AssertionError
```

an argument can be added to the "assert" statement where it returns said argument in the exception message

```
account = 100

# checks to see if account has the proper value
assert account == 50, "account should equal '100'"
>>> AssertionError: account should equal '100'
```

## 0.9.6 - Handling Exceptions With Conditionals

* the else statement can be used to handle exceptions
* it will run its segmented code if no exceptions occur withing the try statement

```
try:
	print(2/0)
	print("This will not print")
	
except ZeroDivisionError:
	print("You can't divide by zero")
	
else: 
	print("This will print if there are no errors")
	
finally:
	print("This will print no matter what")
```

## 0.9.7 - Helpful Summary

If you are still confused, here is a helpful summary

```
try - tries to run a segment of code
except - runs if an error occurs
else - runs if no errors occur
finally - runs no matter what
```