Duplicated string literals make the process of refactoring error-prone, since you must be sure to update all occurrences.

On the other hand, constants can be referenced from many places, but only need to be updated in a single place.

Noncompliant Code Example

With the default threshold of 3:

def run():
    prepare("this is a duplicate")  # Noncompliant - "this is a duplicate" is duplicated 3 times
    execute("this is a duplicate")
    release("this is a duplicate")

Compliant Solution

ACTION_1 = "action1"

def run():
    prepare(ACTION_1)
    execute(ACTION_1)
    release(ACTION_1)

Exceptions

No issue will be raised on:

@app.route("/api/users/", methods=['GET', 'POST', 'PUT'])
def users():
    pass

@app.route("/api/projects/", methods=['GET', 'POST', 'PUT'])  # Compliant
def projects():
    pass