188 – Read file lines until a separator

To read the lines of a file until you hit a predetermined separator, you can use the special form of the built-in function iter, the method readline, and the string literal that matches the separator.

For example, suppose you have this file called names.txt:

Harry
Hermione
Ron
---
Potter
Granger
Weasley

If you want to read lines until you hit the separator "---", you can use the building blocks mentioned:

first_names = []
with open("names.txt", "r") as f:
    for name in iter(f.readline, "---\n"):
        first_names.append(name.strip())

print(first_names[-1])  # Ron

The expression iter(f.readline, "---\n") creates an iterable that calls f.readline — to read a line from the file — repeatedly until f.readline() returns "---\n", the line with the separator. Note how the separator ends with the newline character "\n", since the method f.readline returns lines with the newline characters.