File Writing

Write Mode

  1. # write to file (overwrites)
  2. with open("output.txt", "w") as file:
  3.     file.write("Hello, World!")

Write Multiple Lines

  1. # write several lines
  2. with open("output.txt", "w") as file:
  3.     file.write("Line 1\n")
  4.     file.write("Line 2\n")
  5.     file.write("Line 3\n")

Writelines

  1. # write list of lines
  2. lines = ["Line 1\n", "Line 2\n", "Line 3\n"]
  3. with open("output.txt", "w") as file:
  4.     file.writelines(lines)

Append Mode

  1. # append to existing file
  2. with open("output.txt", "a") as file:
  3.     file.write("Appended line\n")

Write Returns Count

  1. # write returns character count
  2. with open("output.txt", "w") as file:
  3.     count = file.write("Hello")
  4. #ans: count is 5

Exercises - Part 1

  1. # write mode behavior?
  2. with open("file.txt", "w") as f:
  3.     f.write("New content")
  4. #ans: overwrites existing file

Exercises - Part 2

  1. # write adds newline?
  2. with open("file.txt", "w") as f:
  3.     f.write("Line 1")
  4.     f.write("Line 2")
  5. #ans: "Line 1Line 2" (no newline)

Exercises - Part 3

  1. # writelines adds newlines?
  2. lines = ["A", "B", "C"]
  3. with open("file.txt", "w") as f:
  4.     f.writelines(lines)
  5. #ans: "ABC" (no newlines)

Exercises - Part 4

  1. # append to non-existent?
  2. with open("new.txt", "a") as f:
  3.     f.write("Text")
  4. #ans: creates new file

Exercises - Part 5

  1. # write empty string?
  2. with open("file.txt", "w") as f:
  3.     f.write("")
  4. #ans: creates empty file

Exercises - Part 6

  1. # write number?
  2. with open("file.txt", "w") as f:
  3.     f.write(42)
  4. #ans: TypeError (must be string)

Exercises - Part 7

  1. # write return value?
  2. with open("file.txt", "w") as f:
  3.     n = f.write("Hi")
  4. #ans: n is 2

Exercises - Part 8

  1. # write in read mode?
  2. with open("file.txt", "r") as f:
  3.     f.write("Text")
  4. #ans: io.UnsupportedOperation

Exercises - Part 9

  1. # append vs write?
  2. #ans: "w" overwrites
  3. #ans: "a" adds to end

Exercises - Part 10

  1. # write binary?
  2. with open("file.bin", "wb") as f:
  3.     f.write(b"data")
  4. #ans: writes bytes

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