Learn the standard library to at least know what's there

itertools and collections have very useful features

chain
product
permutations
combinations
izip



In [1]:

    
%matplotlib inline
%config InlineBackend.figure_format='retina'

import matplotlib.pyplot as plt
import seaborn as sns
sns.set_context('talk')
sns.set_style('darkgrid') 
plt.rcParams['figure.figsize'] = 12, 8  # plotsize 

import numpy as np
import pandas as pd



In [2]:

    
# plot residuals



In [3]:

    
from itertools import groupby # NOT REGULAR GROUPBY
from itertools import product, cycle, izip
import re # regular expressions

Challenge (Easy)

Write a function to return the total number of digits in a given string, and those digits.



In [5]:

    
test_string = """de3456yghj87654edfghuio908ujhgyuY^YHJUi8ytgh gtyujnh y7"""



In [6]:

    
count = 0
digits = []
for x in test_string:
    try: 
        int(x)
        count += 1
        digits.append(int(x))
    except:
        pass
    
print "Number of digits:", str(count) + ";"
print "They are:", digits









    



Number of digits: 14;
They are: [3, 4, 5, 6, 8, 7, 6, 5, 4, 9, 0, 8, 8, 7]

Challenge (Tricky)

Same as above -- but were consecutive digits are available, return as a single number.

Ex. "2a78b123" returns "3 numbers, they are: 2, 78, 123"



In [7]:

    
test_string









    Out[7]:





'de3456yghj87654edfghuio908ujhgyuY^YHJUi8ytgh gtyujnh y7'



In [8]:

    
groups = []
uniquekeys = []
for k, g in groupby(test_string, lambda x: x.isdigit()):
    groups.append(list(g))
    uniquekeys.append(k)



In [9]:

    
print(groups)
print(uniquekeys)









    



[['d', 'e'], ['3', '4', '5', '6'], ['y', 'g', 'h', 'j'], ['8', '7', '6', '5', '4'], ['e', 'd', 'f', 'g', 'h', 'u', 'i', 'o'], ['9', '0', '8'], ['u', 'j', 'h', 'g', 'y', 'u', 'Y', '^', 'Y', 'H', 'J', 'U', 'i'], ['8'], ['y', 't', 'g', 'h', ' ', 'g', 't', 'y', 'u', 'j', 'n', 'h', ' ', 'y'], ['7']]
[False, True, False, True, False, True, False, True, False, True]



In [10]:

    
numbers = []
for x, y in izip(groups, uniquekeys):
    if y:
        numbers.append(int(''.join([j for j in x])))
print "Number:", np.sum(uniquekeys)
print "They are:", numbers









    



Number: 5
They are: [3456, 87654, 908, 8, 7]



In [11]:

    
# In one cell

def solution_2(test_string):
    groups = []
    uniquekeys = []
    for k, g in groupby(test_string, lambda x: x.isdigit()):
        if k:
            groups.append(int(''.join([j for j in g])))

    return len(groups), groups
    
print solution_2(test_string)









    



(5, [3456, 87654, 908, 8, 7])

Challenge (Tricky)

Same as above, but do it a second way.



In [12]:

    
def solution_3(test_string):
    """Regular expressions can be a very powerful and useful tool."""
    groups = [int(j) for j in re.findall(r'\d+', test_string)]
    return len(groups), groups

solution_3(test_string)









    Out[12]:





(5, [3456, 87654, 908, 8, 7])

Challenge (Hard)

Same as above, but all valid numbers expressed in digits, commas, and decimal points.

Ex. "a23.42dx9,331nm87,55" -> 4; 23.42, 9331, 87, 55

Left as an exercise :)

Don't spend much time on this one.

Generators



In [13]:

    
def ex1(num):
    """A stupid example generator to prove a point."""
    while num > 1:
        num += 1
        yield num



In [14]:

    
hey = ex1(5)



In [15]:

    
hey.next()









    Out[15]:





6



In [58]:

    
hey.next()









    Out[58]:





49

Gotchas

Modifying a dictionary's keys while iterating over it.

for key in dictionary:
    if key == "bat":
        del dictionary[key]

If you have to do something like this:

list_of_keys = dictionary.keys()
for key in list_of_keys:
    if key == "bat":
        del dictionary[key]



In [ ]: