Understanding Functions in Python
Python provides built-in help functionality for getting quick information about functions and statements.
A Question at the Interpreter
When you encounter a Python function or statement that you do not yet understand, you do not always need to leave the interpreter prompt to find basic information. Python provides built-in help functionality for getting quick information about functions and statements. This makes the interpreter prompt a useful place to investigate while learning.
A function is a reusable piece of a program. Python includes built-in functions, such as len and range, that perform useful operations.
Following a Help Request
Consider the source example help('len'). The request begins with help, which is the built-in help functionality. The text len identifies the function about which you want information. Python then displays help for the len function. The important sequence is: request help, identify the function, and read the information Python displays.
Requesting information about len
You want quick information about the len function while working at the Python interpreter prompt.
- 1Make the request
Use the source example
help('len')at the interpreter prompt. - 2Identify the subject
The text len tells Python which function you want to investigate.
- 3Read the result
Python displays help for the len function.
- 4Connect the information to the purpose
The len function is used to count the number of items.
help('len') gives quick information about len, including that it is used to count the number of items.
Reusable Work in Python
Functions matter because they package work that can be used again. The source describes functions as reusable pieces of programs. Instead of treating every operation as unrelated, you can recognize a function as a named piece of program behavior that can be used when that operation is needed.
Python's built-in functions illustrate this idea. The len function is used to count the number of items. The range function is used to generate a sequence of numbers. Each function supports a particular task, so knowing a function's purpose helps you understand what kind of work it performs.
Help and Action
| Expression | Purpose |
|---|---|
| help('len') | Displays help for the len function |
| len | Names the function being investigated |
| len applied to a Python object | Uses len for its counting purpose |
The help request is about learning what len does; len itself is the function used to count the number of items.
This distinction prevents a common confusion. help('len') is a request for information about len. It does not represent the counting purpose described for len. The function being described is len, while help is the tool used to learn about it.
Suppose you are working at the interpreter prompt and remember the name len but not its purpose. Asking for help lets you check the function's role immediately. After reading that len counts the number of items, you have a clearer basis for deciding whether it is relevant to the task you are working on.
Mistakes with Built-In Help
Common mistake Treating help('len') as the counting operation
What it looks likeThe help request is confused with the purpose of len.
Why it failsThe source example says that
help('len')displays help for len, while len is used to count the number of items.Do this insteadSeparate the two roles: use help to obtain information, and recognize len as the function used for counting.
Common mistake Forgetting that functions are reusable pieces of programs
Why it failsThinking of a function as a one-time instruction hides why functions are useful.
Do this insteadRemember that functions are reusable pieces of programs and that built-in functions provide ready-made operations.
Common mistake Assuming every built-in function has the same purpose
What it looks likeConfusing len with range.
Why it failsThe source identifies different purposes: len counts the number of items, while range generates a sequence of numbers.
Do this insteadUse help when you need to check what a particular function does.
When a function name is familiar but its purpose is unclear, use Python's built-in help functionality at the interpreter prompt instead of relying on a guess. Then connect the displayed information to the task the function performs.
Practice the Investigation
At the Python interpreter prompt, you need to find out what len is for. What built-in help request should you use, what information should you expect it to provide, and how is that different from the purpose of len itself?
Hints
- Use the source example involving the text len.
- Separate the act of requesting information from the operation performed by the function.
- Recall the stated purpose of len and compare it with the stated purpose of range.
Checking your reasoning
Explain the roles of help, len, and range without treating them as interchangeable.
- 1Identify help
help provides quick information about a function or statement, especially at the interpreter prompt.
- 2Identify len
len is the function described in the source as being used to count the number of items.
- 3Identify range
range is the built-in function described as generating a sequence of numbers.
- 4Compare the roles
The functions have different purposes, and help is the information tool used to investigate them.
help provides information, len counts the number of items, and range generates a sequence of numbers.
Key Takeaways
- 1Python's built-in help functionality provides quick information about functions and statements.
- 2The interpreter prompt is a useful place to request this information.
- 3The source example
help('len')displays help for the len function. - 4Functions are reusable pieces of programs.
- 5len counts the number of items, while range generates a sequence of numbers.
At a glance
- Use Python's built-in help functionality when you need quick information about a function or statement.
- At the interpreter prompt,
help('len')displays help for the len function. - Functions are reusable pieces of programs, and Python includes built-in functions for specific tasks.
- The len function is used to count the number of items.
- The help request and the function's operation are different: help explains len, while len performs its counting task.