Add lecture 5 File/IO notes

Author: Sahil

README.md

@@ -15,4 +15,4 @@ To discuss any doubts or questions after today's class with the community, join
 - Lecture 2: [[Notes]](/lecture2.md) [[Video]](https://www.youtube.com/watch?v=Q7nvvSlWem4) - Operators, Basic Control Flow - Conditionals, Loops and Functions
 - Lecture 3: [[Notes]](/lecture3.md) [[Video]](https://www.youtube.com/watch?v=tmxCgqNSj88) - Basic Data Structures and Containers: Lists, Tuples, Sets, Dictionaries
 - Lecture 4: [[Notes]](/lecture4.md) [[Video]](https://www.youtube.com/watch?v=NsOzuuLlR08) - Organizing Code & Dependency Management
-- Lecture 5: [[Notes]](/lecture5.md) [[Video]]() - File I/O, reading and writing text, csv and json files
+- Lecture 5: [[Notes]](/lecture5.md) [[Video]](https://www.youtube.com/watch?v=kj61srFJ9fY) - File I/O, reading and writing text, csv and json files

day5/todos.py

@@ -0,0 +1,12 @@
+"""
+The program fetches a json file and deserializes it
+"""
+
+import json
+import requests
+
+URL = "https://jsonplaceholder.typicode.com/todos"
+response = requests.get(URL)
+todos = json.loads(response.text)
+
+print(todos[0])

lecture5.md

@@ -2,12 +2,139 @@
 
 ## Working with Text Files
 
+- Used to store data such that it can be retrieved any time
+- To read or write from a file, the following operations take place:
+1. Open a file
+2. Perform Read or write operations
+3. Close the file
+
+### Open a file
+
+```py
+f = open('hello.txt', 'r')
+```
+
+- First argument is the string containing file name
+- Second argument is the file opening mode. (`r`, `w`, `a`, etc.)
+- Default, files are opened in text mode.
+
+### Reading from file
+
+```py
+f.read(5) # read next 5 bytes
+f.readline() # read the entire line
+f.readlines() # read the entire file and return list of lines
+f.tell() # get the current file position
+f.seek(0) # bring file cursor to initial position
+```
+### Writing to file
+
+```py
+f.write("hello world\n")
+```
+
+### Closing a file
+
+- Frees up the resources tied with the file
+
+```py
+f.close()
+```
+
+- Need to worry about exceptions if any operation on file is running
+- Use a `try...finally` block of code
+
 ## Open file using context manager
 
+- Need not close the file explicitly
+
+```py
+with open('hello.txt') as f:
+  # perform file operations
+```
+
 ## Working with CSV Files
 
+- CSV (Comma Separated Values) format is one of the most simplest ways to store tabular data.
+- Elements are separated by a delimiter, generally, a comma `,`.
+- The python's `csv` module makes it easier to operate on such files.
+
+### Reading CSV File
+
+```py
+import csv
+with open('marks.csv', 'r') as file:
+  reader = csv.reader(file)
+  for row in reader:
+    print(row)
+```
+
+- Explore `skipinitialspace` attribute in the reader function.
+- There can be many other attributes specified and can make code difficult to maintain, so to solve this `dialect` is provided as another optional parameter, which groups together many formatting patterns.
+
+### Writing to CSV File
+
+```py
+import csv
+with open('marks.csv', 'w') as file:
+  writer = csv.writer(file)
+  writer.writerow(["Roll No.", "Name", "Marks"])
+  writer.writerow([1, "abc", 95])
+  writer.writerow([2, "def", 97])
+```
+
+- You can also try creating rowlist as list of lists and use the `writer.writerows` function.
+
+### Read file as a dictionary
+
+```py
+import csv
+with open('marks.csv', 'r') as file:
+  csv_dict = csv.DictReader(file)
+  for row in csv_dict:
+    print(row)
+```
+
+- Similarly, can try exploring `DictWriter`.
+- Also try to explore the `Pandas` library which is a popular library for data manipulation and analysis.
+
 ## Working with JSON Files
 
+- Saving more complex data types like nested lists and dictionaries, parsing and serializing becomes complicated.
+- Python allows us to use the popular data interchange format JSON (JavaScript Object Notation) through a module `json`.
+- Converting python data to string is known as *serializing*.
+- Reconstructing the data from the string representation is called *deserializing*.
+
+### Reading json from file
+
+```py
+import json
+with open('marks.json') as file:
+  data = json.load(file)
+  print(data) # dict
+```
+
+- `json.loads` can be used to convert string to dict.
+
+### Writing json to file
+
+```py
+import json
+
+marks_dict = {
+  "roll_no": 12,
+  "name": "abc",
+  "marks": 99
+}
+with open('marks.json', 'w') as json_file:
+  json.dump(marks_dict, json_file)
+```
+
+- `json.dumps` can be used to convert dict to string.
+- Can pass `indent` and `sort_keys` properties to pretty print the json data.
+
+[Example code](day5/todos.py)
+
 ## Other libraries and documentation
 
 - For manipulating path: [pathlib](https://docs.python.org/3/library/pathlib.html) and [os.path](https://docs.python.org/3/library/os.path.html)