Miscellaneous Python things

In this session, we'll talk about:

More control flow tools: try/except, break and continue
A few other built-in Python functions
Installing third-party modules

Handling errors with try/except

Sometimes your script will throw errors. When it does, sometimes you want the script to continue after handling the error in some way. Let's take a look at some examples.

What happens when we run the code below?



In [ ]:

    
humans = [
    {'name': 'Cody', 'age': 32, 'job': 'Training director', 'height_in': 72},
    {'name': 'Jeff', 'age': 44, 'job': 'Snake charmer', 'height_in': 60},
    {'name': 'Sally', 'age': 55, 'job': 'Fry cook'}
]

for human in humans:
    print(human['name'], 'is', human['height_in'], 'inches tall')

Let's catch the KeyError. You could use a bare except statement, which would fire if any exception is raised, but it's good practice to specify the class of error that you're controlling for.



In [ ]:

    
humans = [
    {'name': 'Cody', 'age': 32, 'job': 'Training director', 'height_in': 72},
    {'name': 'Jeff', 'age': 44, 'job': 'Snake charmer', 'height_in': 60},
    {'name': 'Sally', 'age': 55, 'job': 'Fry cook'}
]

for human in humans:
    try:
        print(human['name'], 'is', human['height_in'], 'inches tall')
    except KeyError:
        print('We don\'t know how tall', human['name'], 'is')

Break and continue

These statements are frequently used in loops to control the flow of your program. We'll use range() to demo how each statement works.

break breaks out of the loop
continue skips to the next iteration



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# break
for x in range(10):
    if x == 7:
        break
    else:
        print(x)



In [ ]:

    
# continue
for x in range(10):
    if x == 7:
        continue
    else:
        print(x)

Other built-in functions

Check out the full list here. We're just going to look at a couple.

`dir()`

Use the dir() function to see all of the attributes and methods available to an object -- this is often how I learn about new ways to manipulate data!

Let's try it out on some different data types.



In [ ]:

    
# string
dir('hello!')



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# lists
l = [1, 2, 3, 4, 5, 6]
dir(l)



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# dicts
d = {'name': 'Cody', 'age': 32, 'job': 'Training director', 'height_in': 72}

dir(d)

`enumerate()`

Use enumerate() in a loop to keep track of where you're at in the loop -- the index. Notice that we then need to use two variables in the loop -- the index and the actual value.



In [ ]:

    
humans = [
    {'name': 'Cody', 'age': 32, 'job': 'Training director', 'height_in': 72},
    {'name': 'Jeff', 'age': 44, 'job': 'Snake charmer', 'height_in': 60},
    {'name': 'Sally', 'age': 55, 'job': 'Fry cook'}
]

for idx, human in enumerate(humans):
    print(idx, human['name'])

`zip()` and `dict()`

Use zip to fold multiple iterable objects into one thing. My favorite use of zip is turning two lists of related data into a single dictionary using dict() to coerce the zip object:



In [ ]:

    
names = ['Cody', 'Jeff', 'Sally']
ages = [32, 44, 55]

zip_obj = zip(names, ages)

human_dict = dict(zip_obj)

print(human_dict)

`sum()`, `max()` and `min()`

Sum a list of numbers
Find the highest value in a list
Find the lowest value in a list



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# a list of numbers
l = [1100, 200, 9400, 800, 1000]

# sum
total = sum(l)

# max
max_value = max(l)

# min
min_value = min(l)

# print the results
print(total, max_value, min_value)

Installing third-party packages

Use the pip package manager to install third-party packages. The pip tool comes bundled with Python 3. To install a module system-wide, you'd run this command from the Terminal app: pip install name_of_your_package.

A saner approach would be to use a "virtual environment" and install dependencies specifically for each project. That way, you avoid the problem of "I need version X of pandas for this project but version Y for this other project." If pandas is installed globally on your computer, you'll quickly run into problems.

For this boot camp, we have installed these packages:

jupyter
bs4 (Beautiful Soup)
requests
pandas
matplotlib

Each of these packages, in turn, has dependencies that are automatically installed.

Miscellaneous Python things

Handling errors with try/except

Break and continue

Other built-in functions

dir()

enumerate()

zip() and dict()

sum(), max() and min()

Installing third-party packages

`dir()`

`enumerate()`

`zip()` and `dict()`

`sum()`, `max()` and `min()`