Notes for Session 02¶
April 16, 2019¶
NOTE: These notes are “live” – they will change up until the class starts..
A collection of notes to go over in class, to keep things organized.
Lightning Talks¶
Up today:
Cole Garvens Phalen
Brian Scott Ervin
Are you ready? We’ll do them in the middle of the session.
Class Outline¶
git / gitHub¶
In general, most of you seem to have got the basics down:
- creating a new file
- adding it to git
- pushing it to your fork of the class repo
- making a “pull request” on gitHub.
Any conceptual questions?
Issue:
- Quite a few folks have changed or added files that they should not have:
- The central readme in the students folder
- and extra file here or there
- etc….
git is very flexible, and does not lose data easily. However, it is much harder to undo things than it is to make changes. So you will be happier if you take some extra care to not commit changes that you don’t want. Some hints:
- Always do a
git statusbefore you commit – make sure that the stuff you are going to commit is what you want!- note that if you do
git commitit will only commit those files listed under “staged for commit”. But if you dogit commit -a(-a for all) then it will commit everything modified, i.e. “Changes not staged for commit:”.
- note that if you do
Note in the status report:
$ git status
On branch master
Your branch is up to date with 'origin/master'.
Changes not staged for commit:
(use "git add <file>..." to update what will be committed)
(use "git checkout -- <file>..." to discard changes in working directory)
modified: notes_for_class/source/session02.rst
...
It even tells you want to do: use git add to stage particular files, or git checkout to revert a file back to its state as of the last commit.
It doesn’t mention git commit -a, but that will commit everything that is “not staged for commit”.
If you are careful before the commit stage, then you won’t have to “roll back” changes very often.
But if you do:
Let’s play around with that a bit.
Exceptions¶
Most of you seemed to do fine making the few key exceptions – any questions?
Note:
We were not expecting you to catch the exceptions – we’re really starting at the bottom here, just making sure you get used to seeing Exceptions, and what they mean.
We’ll get into Exception handling later.
Coding Bat¶
The assert statement¶
This is a good time to learn about assert
assert is used primarily for testing; it is a quick way to make sure that something is True.
If whatever follows the assert is True, it is silent. If it is not True, an AssertionError is raised:
In [4]: assert 4 == 4
In [5]: assert 4 == 5
---------------------------------------------------------------------------
AssertionError Traceback (most recent call last)
<ipython-input-5-0e54103c2322> in <module>
----> 1 assert 4 == 5
AssertionError:
If you follow the expression after the assert with a string, it will get passed along with the AssertionError
In [8]: assert 4 == 5, "4 and 5 aren't equal"
---------------------------------------------------------------------------
AssertionError Traceback (most recent call last)
<ipython-input-8-dc75c89b2172> in <module>
----> 1 assert 4 == 5, "4 and 5 aren't equal"
AssertionError: 4 and 5 aren't equal
I rarely do that – it’s usually obvious what when wrong …
We will learn more formal testing in a couple weeks, but you can make some quick tests with asserts to check your code.
Handy for codingbat:
# String-2 count_code
# Example from codingbat: https://codingbat.com/prob/p186048
def count_code(str):
count = 0
for i in range(len(str) - 3):
if str[i:i + 2] == "co" and str[i + 3] == "e":
count += 1
return count
assert count_code('aaacodebbb') == 1
assert count_code('codexxcode') == 2
assert count_code('cozexxcope') == 2
assert count_code('cozexxcope') == 2
assert count_code('cozfxxcope') == 1
assert count_code('xxcozeyycop') == 1
assert count_code('cozcop') == 0
print("all checks passed")
Shall we try a couple?
- maybe “front3” – start with Rimlee’s solution?
Anyone stuck on any of them?
Anyone not like their solution?
Let’s talk about it!
Lightning Talks¶
Let’s take a break and do some lightning talks…