Startswith, endswith. All Python strings have a start and an end. Often we need to test the starts and ends of strings. We use the startswith and endswith methods.

We can take a substring and compare that to a string—this can do the same thing as startswith or endswith. But with specialized methods, our code is clearer and likely faster.

Substring

Example. Here we have a string that has many characters in it. We want to see what prefixes and suffixes may match. We use several if-statements.

if

not

phrase = "cat, dog and bird"

# Step 1: see if the phrase starts with this string.
if phrase.startswith("cat"):
    print(True)

# Step 2: a longer prefix.
if phrase.startswith("cat, dog"):
    print(True)

# Step 3: it does not start with this string.
if not phrase.startswith("elephant"):
    print(False)

# Step 4: test the end of the string.
if phrase.endswith("bird"):
    print("Ends with bird")

# Step 5: does not match.
if phrase.endswith("?") == False:
    # Does not end in a question mark.
    print(False)
True
True
False
Ends with bird
False

Some notes, performance. In my performance testing, I have found Python tends to be fastest when the minimal number of statements and method calls are made.

With string-testing methods like startswith and endswith, we can check the beginning and ends of strings. This can avoid complexity in code.