File IO

Reading Files

Python has a built-in function called open() that allows you to open and read files. The open() function takes two arguments: the name of the file and the mode in which you want to open the file. The mode can be r for reading, w for writing, or a for appending.

# Syntax
file = open("filename", "mode")

# Example
file = open("example.txt", "r")

In the example above, we open a file called example.txt in read mode.

Reading the Entire File

You can read the entire contents of a file using the read() method.

# Syntax
file.read()

# Example
file = open("example.txt", "r")
content = file.read()
print(content)

In the example above, we read the entire contents of the file example.txt and store it in a variable called content. We then print the contents of the file to the console.

Reading Line by Line

You can also read the contents of a file line by line using the readline() method.

# Syntax
file.readline()

# Example
file = open("example.txt", "r")
line1 = file.readline()
line2 = file.readline()
print(line1)
print(line2)

In the example above, we read the first two lines of the file example.txt and store them in variables called line1 and line2. We then print the contents of the variables to the console.

Closing Files

After you have finished working with a file, you should close it using the close() method.

# Syntax
file.close()

# Example
file = open("example.txt", "r")
content = file.read()
file.close()

In the example above, we open the file example.txt, read its contents, and then close the file.

Alternatively, you can use the with statement to open and close files automatically.

# Example
with open("example.txt", "r") as file:
    content = file.read()

In the example above, the file is automatically closed when the with block is exited.

Writing to Files

You can write to files using the write() method.

# Syntax
file.write("text")

# Example
with open("example.txt", "w") as file:
    file.write("Hello, world!")

In the example above, we open the file example.txt in write mode and write the text "Hello, world!" to the file.

Appending to Files

You can append to files using the write() method with the a mode.

# Example
with open("example.txt", "a") as file:
    file.write("Hello, again!")

In the example above, we open the file example.txt in append mode and write the text "Hello, again!" to the file.

Working with CSV Files

Python has a built-in module called csv that allows you to read and write CSV files.

# Example
import csv

with open("example.csv", "r") as file:
    reader = csv.reader(file)
    for row in reader:
        print(row)

In the example above, we use the csv module to read the contents of a CSV file called example.csv and print each row to the console.

You can also write to CSV files using the csv.writer class.

# Example
import csv

with open("example.csv", "w") as file:
    writer = csv.writer(file)
    writer.writerow
    writer.writerow(["Name", "Age"])
    writer.writerow(["Alice", 25])
    writer.writerow(["Bob", 30])

In the example above, we use the csv.writer class to write data to a CSV file called example.csv. We first write the column headers, and then write the data for each row.

Other File Formats

Python has built-in support for working with other file formats such as JSON, XML, and more. You can use third-party libraries to work with these file formats as well.

# Example
import json

data = {
    "name": "Alice",
    "age": 25
}

with open("example.json", "w") as file:
    json.dump(data, file)

In the example above, we use the json module to write a Python dictionary to a JSON file called example.json.