Reading and Writing Files: Handling Text and Data Efficiently

Reading from a File

To start reading a file, you first need to open it in the appropriate mode. Here's how you can open and read from a file:

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file = open("greetings.txt", "r")
print(file.read()) # Output:
# Hello, world!
# Salut!
# Hola!
file.close()

Reading Specific Characters

You can also read a specific number of characters by passing a numeric argument to the read method:

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file = open("greetings.txt", "r")
print(file.read(10))  # Output: Hello, wor
file.close()

Reading Line by Line

To read a file line by line, you can use a loop along with the readline() or readlines() methods. The readline() method returns a string for each line, while readlines() returns a list of all lines:

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file = open("greetings.txt", "r") # ['Hello, world!\n', 'Salut!\n']
print(file.readline())  # Output: Hello, world!
print(file.readline())  # Output: Salut!
file.close()

For more efficient line-by-line reading without loading the entire file into memory, use a for loop with readlines():

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file = open("greetings.txt", "r")
for line in file.readlines():
    print(line, end="")  # The `end=""` argument prevents adding extra line breaks
# Output:
# Hello, world!
# Salut!
# Hola!
file.close()

Writing to a File

To write data to a file, you should open it in write mode ('w'). Only strings can be passed to the write() method.

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file = open("greetings.txt", "w")
file.write("Bonjour!")
file.close()

Note

The writing mode overwrites the existing file content.

In this case, any existing data in "greetings.txt" will be replaced with "Bonjour!"