Lesson 5
Writing Reusable and Self-explanatory Programs
Chapter 5: Advanced function features
Default arguments
Python also allows you to provide default arguments, so that the poor user (that includes you!) does not have to explicitly provide a value for every single parameter.
def do_something(a, b, c=2, d="great", e=5, f="john", g="python", h=-1, i=0, j=2):
print(f"{a}; {b}; {c}; {d}; {e}; {f}; {g}; {h}; {i}; {j}")
return None
Users calling the function must provide the first two positional arguments. Then they can optionally provide any additional arguments that they need. Anything else not given will use the default arguments that the function defined.
>>> x = do_something("first", "second")
first; second; 2; great; 5; john; python; -1; 0; 2
>>> x = do_something("first", "second", "arg for c", "arg for d")
first; second; arg for c; arg for d; 5; john; python; -1; 0; 2
The following function definition is not allowed. Why?
def my_function(a="first", b, c, d="default d"):
print(f"{a}; {b}; {c}; {d}")
Try it out! It will result in a syntax error. The error message should tell you exactly why.