Computer Science for STEM The PreTeXt Interactive Edition

We previously used a few functions like print() and len() where we place the variable inside the parentheses such as len(my_str). On the other hand, a method is a function that is attached to a specific Python object. To access this function, we write the object, then a dot ., and then the name of the method. The "dot notation" is the way we connect the name of an object to the name of a method it can perform. For example, we can write my_str.upper() when we want the string my_str to perform the upper() method to create an upper-case version of itself.

Remember that strings are immutable. Therefore, all string methods give us a new string and must be assigned to a new variable. The original string is unchanged.

In this example, upper is a method that can be invoked on any string object to create a new string in which all the characters are in uppercase.

In addition to upper, the following table provides some useful string methods.

You should experiment with these methods so that you understand what they do. Note once again that the methods that return strings do not change the original.

Check your understanding

s = "python rocks"
print(s.count("o") + s.count("p"))

s = "python rocks"
print(s[1] * s.index("n"))