Python-Intermediate-Notes

Handling Creating Writing to a File

Files

Files are the named locations where you securely store your data

Types of Files

  1. Binary Files - are used for storing media files, compiled code, or app data.
  2. Text Files - are readable to use (plain text, source code)

Functions used for files

open() function parameters

open() function has two parameters: 
    open(filename, mode)

How do we open a file?

r(read), a(append), w(write), x(create)

f = open("newfile.txt", "x") #x used to create new files

f = open("newfile.txt", "w") #w opens the files for us to write. Also overwwrite existing content
f.write("Python is easy!") #It can also be used to create new files. 

f = open("newfile.txt", "r") 
print(f.read())
f.close()

f= open("newfile.txt", "a") #a appends, or adds, to something. It can also used to create a new file

f.write("Python Intermediate")

f = open("newfile.txt", "r") 
print(f.read())
f.close()

Reading from a file

r(read) - default value for python FileNotFoundError - if the file doesn’t exist

f = open("newfile.txt", "rt") #access file

or

f = open("newfile.txt")

Example

f = open("newfile.txt", "r") #file is an object
print(f.read()) #file more 'r' return the whole text.

Reading specific parts of a files

f = open("newfile.txt", "r")
print(f.read(12))

readline() - returns a single line

f = open("newfile.txt", "r")
print(f.readline())

for loops - allows to read the whole file one line at a time

for x in f:
    print(x)

always close the files

f.close()

Deleting a file

if not sure if the file exist

import os

if os.path.exists("newfile.txt"):
    os.remove("newfile.txt")
else:
    print("The files doesn't exists")

if sure the file exists

import os
os.remove("newfile.txt")

Exceptions

Exception - is an object which tell you about the problem you encountered. It also provibes a traceback, which tells you specifically where you made a blunder in your code.

Built-in excetions

  1. raise keywoard - lets us throw an excetion. We can use it to define the error we’d like to raise, and what text will be printed on the console

Example: we dont want any negative values

n = -5
if n < 0:
    raise Exception("No negative numbers allowed")

  1. syntax error - occurs when the code is not written correctly

  2. assertions - boolean expressions that make sure that the conditions are true.

Example: ``` employee_of_the_year = “Roger”

assert employee_of_the_year == “Roger” #can also be used for debugging tool because its stops the program as soon as an error occur assert employee_of_the_year == “Shane” #error because we also assign shane as employee of the year


4. ZeroDivisionError - occurs when you divide by zero

> Example:

1/0


5. TypeError - occurs when an operation is performed on an incorrect or unsupported object type. 

> Example:

50 ** “two”


## How we can handle them? 
**try except** - these blocks are used to spot and handle exceptions

**try** - test the code to ensure that there are no errors

**except** - if we don't handle an exception with an except block, the program will crash

**finally** - finally block allows us to run our code no matter what the result of the try and except blocks is

Example:

try: print(random_var) except: print(“Exception Alert!”)

try: print(x + “macarons”) except NameError: print(“Please define your variable”) except IndentationError: print(“Please be careful with your identing your code.”) except: print(“Something else went wrong. We need to figure it out.”)

try: print(24 + 42) except: print(“This operation cannot be performed”) else: print(“No issues here!”)

try: print(n) except: print(“There something wrong with our program.”) finally: print(“Let’s run our program anyway”) #run our code even there’s error ```

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