{ Useful Python Modules. }
Objectives
By the end of this chapter, you should be able to:
- Distinguish between the different types of imports
- Give examples of advanced data types provided by the
collectionsmodule
Now that you know how to import, let's examine a few useful modules:
Random
The random module is quite useful for generating random values of all kinds:
import random random.randint(1,10) # generate a number between 1 and 10 random.randrange(4) # generate between 0 and 3 random.random() # generate a number between 0 and 1
Here's an example pulling just a single function, the choice function, which grabs an element at random from a list:
from random import choice as c c([1,2,3,4,5]) # run this line several times, you should see different elements get returned
Math
The math module provides access to many mathematical functions, including helpers for rounding, constants like e and pi, and trigonometric functions.
import math math.e # 2.718281828459045 math.pi # 3.141592653589793 math.floor(2.2) # 2 math.ceil(2.2) # 3 math.sqrt(16) # 4 math.pow(2,10) # 1024.0
Collections
This is a built in module that provides alternatives to Python's built-in containers like dict, list, set, and tuple. Take a look at each one of these and see what they do.
Counter
from collections import Counter l = [1,1,2,3,3,4,4,5,5] Counter(l) # see what this returns! string = "aweosakjdsaldwjdwq" Counter(string) s = 'this is such a nice nice nice thing that is nice!' c = Counter(s.split()) # Counter({'a': 1, # 'is': 2, # 'nice': 3, # 'nice!': 1, # 'such': 1, # 'that': 1, # 'thing': 1, # 'this': 1}) c.items() # list of element,count tuples c.clear() # clear all values c.values() # see all values
Defaultdict
from collections import defaultdict regular_dict = dict(first=1) regular_dict['first'] # 1 regular_dict['second'] # KeyError! def default_value(): return "nothing" d = defaultdict(default_value) d['nice'] = "cool" d['nice'] # "cool" d['whoaaa'] # "nothing"
OrderedDict
An ordered dictionary remembers the order in which key-value pairs were added.
from collections import OrderedDict d = {} d['one'] = 1 d['two'] = 2 d['three'] = 3 d['four'] = 4 for k,v in d.items(): print(k,v) # no order! od = OrderedDict() od['one'] = 1 od['two'] = 2 od['three'] = 3 od['four'] = 4 for k,v in od.items(): print(k,v) # order!
namedtuple
from collections import namedtuple t = (1,2,3) t[1] = 2 Person = namedtuple('Person', 'first_name last_name fav_color') elie = Person('Elie', 'Schoppik', 'purple') elie.fav_color # 'purple'
When you're ready, move on to Debugging and Modules Exercises
