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003 Help

Introduction

Purpose

In this notebook, we will learn how to get useful information on python commands using help() and associated methods.

We will use help(list) as an example to learn about the class list from the help material. You are not expected to learn everything about lists here, as we will return to it later in the course. But you should find this useful in learning how to learn.

We will learn how to access some on-line resources.

Prerequisites

You will need some understanding of the following:

Help Method

help()

You can get help on an object using the help() method. This will return a full manual page of the class documentation. You need to gain some experience in reading these and understanding some of the terminology. 

#the method help()
help(list.append)

Help on method_descriptor:

append(self, object, /)
    Append object to the end of the list.

Exercise 1

  • In a new code cell, type help(list) and look through the information provided.

You need to have some practice in interpreting this sort of information.

Scanning the above, we notice for example:

  • list is a class in python
  • It has some methods such as append(self, object, /) and clear(self, /).

We now create two object instances of a list class:

alist = [1, 2, 3]
blist = [4, 5, 6]

and apply methods we see in the Help documentation, here: append() and clear():

alist = [1, 2, 3]
blist = [4, 5, 6]

# append blist as the last element of alist
alist.append(blist)
print('alist =', alist)

# clear blist
blist.clear()
print('blist =', blist)

alist = [1, 2, 3, [4, 5, 6]]
blist = []

Exercise 2

  • Read through the help information for list, above.

  • In a new cell, create lists called alist and blist:

    alist = ['one','three','two']
blist = ['four','six','zero']

  • print the lists with:

    print(alist,blist)

Using the help information, work out how to:

  • extend alist with blist to create ['one','three','two','four','six','zero']. N.B. This is not quite the same as our use of append() above.
  • sort the new alist into alpabetical order and print the results

online help

Not surprisingly, there is lots of help online. A key resource is www.python.org. Another useful one is www.w3schools.com/python:

A useful forum you can search for help on coding problems is https://stackoverflow.com, for example https://stackoverflow.com/search?q=help+on+python+lists, but not all posts are equally useful: pay attention to comments from other users on any answer, as well as post votes. Do not look on stackoverflow until you have exhausted simpler help methods.

help?

You can get a shorter set of basic help by putting ? after the object.

In a notebook, this will show in a new window at the bottom of the book. You can get rid of this by clicking the x.

list?

Learning new things

Let's use that knowledge to learn something new:

Exercise 3

  • Find help for the class range to understand how to use this to generate a sequence of integers from 10 to 1 in steps of -1
  • Use what you have learned to write a for loop below that counts backwards from 10 to 0

Summary

In this session, we have learned some different ways to access help on the operation and options for python commands. These include: help(), use of ? and using online help. Practically, you may use one or more of these methods to find out how something works, or get some examples. We have come across the following commands:

command purpose
help(m) print document string for method m
m? print short document string for method m

We have also touched upon the following commands in the exercises:

command purpose
list Python data type for lists
list.append() append item to list
list.clear() clear item from list
list.sort in-line list sort
range(start,stop,step) list-like generator for integers from start to (but not including) stop in steps of step

You might notice that there are many online forums you can post to to get advice on coding, and we mention https://stackoverflow.com as an example. Remember that not all posts are equally useful: pay attention to comments from other users on any answer, as well as post votes. Do not look on stackoverflow until you have exhausted simpler help methods. You should not generally be posting on these in this course. You will find answers to all that you need in these notes or on existing online pages. You most certainly must not post on forums asking questions about anyt exercises you need to complete or work you need to submit. The course administrators may monitor this.

You should know how to get help on Python functions

You should know how to learn about how to use a particular function, through reading the help information. Take notice of the formatting of this, as you will need to be writing your own help statements later in the course.

You should know how to use the Python function range() and understand teh basics of how to use the Python list data type.

If you are unsure of any of these, then try going over the material again, explore other resources you may find, and/or come to the Thursday help sessions and ask for help.

Last update: September 29, 2021