↑ Python

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Python - Read and Write Files

[!WARNING] Remember to close a file after opening it or use with (see bellow)

file = open("file_name.ext", mode)
file.close()

There are four modes for opening a file:

• r: Read - default, open a file for reading, error if it does not exist
• w: Write - overwrites a file if it exists if not creates it
• a: Append - appends at the end of the file without overwriting it, creates it if does not exist
• x: Create - create a file, error if it already exists

You can also specify if the file should be handle as binary or text (default) using b or t

file = open("file_name.ext", "rt")
file.close()

Read entirely a file

file = open("my_file.md")
content = file.read()
file.close()

Read line by line with a loop

file = open("my_file.md")
for line in file:
  print(line, end=" ") # end=" " avoid doubles line breaks
file.close()

Read a limited number of characters

file = open("my_file.md")
content = file.read(20)
file.close()

Read multiple lines

file = open("my_file.md")
content = file.readlines() # returns a list of lines
for line in content:
  print(line.strip()) # strip() to remove spaces and line breaks
file.close()

Write in a file

• write(): writes a string in a file
• writelines(): writes using a list of string (one per line) in a file

# Write
file = open("my_file.md", "w")
file.write("Hello world!\n")
file.write("Second line")
file.write("Third line\nFourth line")
file.write("""Block of text
New line
  Tabulation
""")

# Write lines
lines = ["First line\n", "Second line"]
file.writelines(lines)
file.close()

# Append
file = open("my_file.md", "a")
file.write("New line at the end of the file\n")
file.close()

Good practice: use with

Using with allows automatic file opening and closing, even if an error is raised.

with open("my_file.md") as file:
  content = file.read()