Functions

Functions

• evit repetition
• scope and local function

def func():
    a = []
    for i in range(5):
        a.append(i)

a

NameError: name 'a' is not defined

# making the function global to fix it

#a = None

def bind_a_variable():
    global a
    a = []
    bind_a_variable()
    
print(a)

None

c = []
def func1():
    for i in range(5):
        c.append(i)

c

[0, 1, 2, 3, 4]

returning multiple values

def f():
    a = 5
    b = 6
    c = 7
    return a, b, c

a, b, c = f()

f()

(5, 6, 7)

f(1, 2, 3)  # traceback because 0 positional argument should have been provided

TypeError: f() takes 0 positional arguments but 3 were given

def g():
    a = 5
    b = 3
    c = 5
    return {'a':a, 'b': b, 'c': c}

g()

{'a': 5, 'b': 3, 'c': 5}

states = ["   Alabama ", "Georgia!", "Georgia", "georgia", "FlOrIda",          "south   carolina##", "West virginia?"]

### data cleaning with functions

import re

def clean_strings(strings):
    result = []
    for value in strings:
        value = value.strip()
        value = re.sub("[!#?]", "", value)
        value = value.title()
        result.append(value)
    return result

clean_strings(states)

['Alabama',
 'Georgia',
 'Georgia',
 'Georgia',
 'Florida',
 'South   Carolina',
 'West Virginia']

lambda functions

def short_function(x):
    return x * 2

equiv_anon = lambda x: x * 2

short_function(3)

6

equiv_anan = 2

def apply_to_list (some_list, f):
    return [f(x) for x in some_list]

ints = [4, 0, 1, 4, 6]
apply_to_list (ints, lambda x: x * 2)

[8, 0, 2, 8, 12]

strings = ['foo', 'card', 'bar', 'aaa', 'abab']

strings.sort(key = lambda x : len(set(x)))

strings

['aaa', 'foo', 'abab', 'bar', 'card']

Generators

some_dict = {'a': 1, 'b': 2, 'c': 3}

for key in some_dict:
    print(key)

a
b
c

dict_iterator = iter(some_dict)

dict_iterator

<dict_keyiterator at 0x193c70f6040>

list(dict_iterator)

['a', 'b', 'c']

tuple(dict_iterator)

()

def squares(n = 10):
    print(f"Generating squares from 1 to {n **2}")
    for i in range (1, n + 1):
        yield i ** 2

gen = squares()

gen

<generator object squares at 0x00000193C6733120>

# use for loop to see the output from generator
for x in gen:
    print(x, end= ' ')

Generating squares from 1 to 100
1 4 9 16 25 36 49 64 81 100 

Generator expressions

gen2 = (x ** 2 for x in range(100))

gen2

<generator object <genexpr> at 0x00000193C6733D60>

for x in gen2:
    print(x, end= " ")

0 1 4 9 16 25 36 49 64 81 100 121 144 169 196 225 256 289 324 361 400 441 484 529 576 625 676 729 784 841 900 961 1024 1089 1156 1225 1296 1369 1444 1521 1600 1681 1764 1849 1936 2025 2116 2209 2304 2401 2500 2601 2704 2809 2916 3025 3136 3249 3364 3481 3600 3721 3844 3969 4096 4225 4356 4489 4624 4761 4900 5041 5184 5329 5476 5625 5776 5929 6084 6241 6400 6561 6724 6889 7056 7225 7396 7569 7744 7921 8100 8281 8464 8649 8836 9025 9216 9409 9604 9801 

# verbose generator

def _make_gen():
    for x in range(100):
        yield x** 2

gen = _make_gen()

# using gen expressions as function arguments

sum (x ** 2 for x in range(100))

328350

dict((i, i**2 ) for i in range(5))

{0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

itertools module

• contains collection of generators for many data algorithms

import itertools

def first_letter(x):
    return x[0]

names =  ['Alan', 'Adam', 'Wes', 'Will', 'Albert']

for letter, names in itertools.groupby(names, first_letter):
    print(letter, list(names))

A ['Alan', 'Adam']
W ['Wes', 'Will']
A ['Albert']

Errors and exception handling

def attempt_float(x):
    try:
        return float(x)
    except:
        return x

1.22

attempt_float('flower')

'flower'

def attempt_float1(x):
    try:
        return float(x)
    except(TypeError, ValueError):
        return x

attempt_float1('nice')

'nice'