Wrap Up#
Some (extra) Python#
string formatting (
format)sets
collectionsargs & kwargs
list comprehensions
map
…or: a day of shortcuts
Note: Shortcuts make your life easier, but your code less understandable to beginners.
It’s hard to search for things you don’t know exist.
Today’s goal : let you know these things exist.
NOT today’s goal : teach you all the details.
You do not need to incorporate these into your project, but if they’ll help you, go for it!
import antigravity
String Formatting#
Use the format method to manipulate and format strings.
name = "Eric"
job = "Lecturer"
topic = "Python"
"Hello! My name is {}. My job is {}, and I work on {}".format(name, job, topic)
Sets#
Sets are a variable type that store only unique entries.
my_set = set([1, 1, 2, 3, 4])
my_set
Like lists, they are iterable & mutable.
my_set.add(2)
my_set
Reminder that if you add a value that is already in the set…the set will not change
Collections#
The collections module has a number of useful variable types, with special properties.
These are “special editions” of collections we’ve discussed before (lists, tuples, and dictionaries).
from collections import Counter
# count how many elements there are in collection
# return values in a dictionary
Counter([1, 0, 1, 2, 1])
import collections
collections.Counter([1, 0, 1, 2, 1])
# can count how many of each letter are in there
Counter("I wonder how many times I use the letter 'e'")
Think back to our encryption scheme!
The most common letter in the English language is ‘e’.
If you just move each letter over by 1 position, you can just use a Counter to crack the code.
Why we moved to a variable encoder!
args & kwargs#
allow you to pass a variable number of arguments to a function
*args- allow any number of extra arguments (including zero)**kwargs- allow any number of keyword arguments to be passed (as a dictionary)
*args#
# use *arguments to demonstrate args
def tell_audience(*arguments):
for arg in arguments:
print(arg)
tell_audience('asdf', 'hello', 'bleargh')
tell_audience("Hello!",
"My name is Eric.",
"My job is Lecturer.")
**kwargs#
def tell_audience_kwargs(**info):
print("type: ", type(info), '\n')
for key, value in info.items():
print("key: ", key)
print("value: ", value, "\n")
tell_audience_kwargs(first='Eric',
last='Morgan',
email='e1morgan@ucsd.edu')
List Comprehensions#
List comprehensions allow you to run loops and conditionals, inside lists.
The general format is :
[ expression for item in list if conditional ]
# NOT a list comprehension
# how we've been doing it
input_list = [0, 1, 2]
output_list = []
for ind in input_list:
output_list.append(ind + 1)
# look at output
output_list
# This list comprehension is equivalent to the cell above
# note the square brackets on the outside
[ind + 1 for ind in [0, 1, 2]]
# You can also include conditionals inside a list comprehension
[val for val in [1, 2, 3, 4, 5] if val % 2 == 0]
Note: there are also tuple & dictionary comprehensions. They’re just used less frequently.
Regular Expressions#
Regular expressions allow you to work with specified patterns in strings.
import re
my_string = "If 12 Python programmers try to complete 14 tasks in 16 minutes, why?"
# can just search for a letter - note that the 'r' in front of the string
# changes it to a "raw string literal", needed to avoid complaints by re when using backslashes
re.findall(r'o', my_string)
# but the patterns are where these shine
re.findall(r'\d\d', my_string)
Lambda Functions#
Lambda functions are small, anonymous functions.
Can define them in line.
increment = lambda a: a + 1
increment(56)
# not a lambda function
def lambda_equivalent(a):
output = a + 1
return output
lambda_equivalent(1)
Another example - here we are trying to sort a list of pairs by the second value in the pair:
def find_key(x):
return x[1]
a = [(1, 7), (4, 2), (3, 8), (1, 5)]
a.sort(key=find_key)
print(a)
a = [(1, 7), (4, 2), (3, 8), (1, 5)]
a.sort(key=lambda x: x[1])
print(a)
map#
map applies a given function to each element in a collection.
# create a function
def double_it(val):
return val * 2
# map function to each element of list
my_list = [1, 2, 3, 4]
list(map(double_it, my_list))
# the above example is equivalent to:
new_list = []
for item in my_list:
new_list.append(double_it(item))
print(new_list)
# Note - we can use lambda functions with map|
list(map(lambda x: x *2, my_list))
Python file operations:#
Opening a file:#
with open('workfile', 'r+', encoding="utf-8") as f: line = f.readline()
filepath = '../temp/'
filename = 'myniftyfile.txt'
with open(filepath + filename, 'r+', encoding="utf-8") as f:
for line in f:
print(line)
open?
line = 'blahblah,stuff\n'
line = line.rstrip()
line = line.split(',')
print(line)
line[1]
The Goal#
To teach you a skill - of how to do things with Python.
You’ve been more formally trained than many people out in the world programming.
Where We’ve Been:#
Python & Jupyter
Variables
Operators
Conditionals
Functions
Lists, Tuples & Dictionaries
Loops
Objects & Classes
Command Line
Scientific Computing
Documentation, Code Style, Code Testing
Class Question #1#
After COGS 18, I feel ____________ my Python programming abilities
A) very confident in
B) somewhat confident in
C) middle-of-the-road about
D) somewhat unsure about
E) very unsure about
Class Question #2#
After COGS 18, I feel the following about my future Python programming:
A) will use again for sure
B) may use again
C) unsure if will use again
D) probably won’t use again
E) definitely won’t use again
How to Continue with Coding#
Write Code
Read Code
Learn and follow standard procedures
Do code reviews
Interact with the community
Build a code portfolio
Powered by Python#
This course used:
Python Programming Language
Jupyter Notebooks
RISE Jupyter Slides
nbgrader
Jupyter Book
scipy stack & many other 3rd party modules
Where do you go from here#
if want_more_data_science:
go to COGS 9
if you want to do more_data_science:
…and Python: take COGS 108
…and R: take COGS 137
if interested_in_research:
look for labs, tell them you can code
if you want_something_else:
go do it!
Acknowledgments#
Thank you to Tom for his original design of this course, and Shannon for her work
Thank you to the TAs and IAs for their tireless work on this class.
Thank you students for you time, effort and patience.