This Python Lambda lesson is for a beginner. Read the short notes, run each example, then change one name or number and run it again.
A lambda is a one-expression function without a name. It fits a sort key or another short callback.
When the logic needs more than one line, write a def. A named function is easier to test and to read a week later.
Example 1: Start here
The minus sign sorts from high to low. lambda score: score would sort from low to high.
scores = [61, 82, 90] # a list; the values stay in this order
scores.sort(key=lambda score: -score) # sort this list in place
print(scores)
Example 2: A one-line function
lambda creates a small function with one expression and no name of its own.
double = lambda n: n * 2 # a one-line function
print(double(6))
Example 3: Sort with a key
The key function tells sort which value to compare.
rows = [{"name": "Arun", "score": 74}, {"name": "Meera", "score": 82}] # a list; the values stay in this order
rows.sort(key=lambda row: row["score"]) # sort this list in place
print([row["name"] for row in rows]) # in is True when the value is found
Example 4: Prefer def when it grows
Use def as soon as the function needs more than one line or a clear name.
def double(n): # define the function; it runs when you call it
return n * 2 # send this value back to the caller
print(double(6))
The minus sign sorts from high to low. lambda score: score would sort from low to high.
