5.1.1 Conda

• Package manager for any language
  
• Install binaries

5.1.2 PIP

• Package manager python only
  
• Compile from source
  
• Stands for Pip Installs Packages
  
• Python’s officially-sanctioned package manager, and is most commonly used to install packages published on the Python Package Index (PyPI)
  
• Both pip and PyPI are governed and supported by the Python Packaging Authority (PyPA).

5.2.1 Import Entire Library

import math
math.sqrt(9)

#:> 3.0

import math as m
m.sqrt(9)

#:> 3.0

from <libName> import *

5.2.2 Import Specific Function

from math import sqrt
print (sqrt(9))

#:> 3.0

Use as for aliasing function name

from math import sqrt as sq
print (sq(9))

#:> 3.0

5.2.3 Machine Learning Packages

alt text

5.3.1 Function Arguments

By default, arguments are assigned to function left to right

def myfun(x,y):
    print ('x:',x)
    print ('y:',y)
    
myfun(5,8)

#:> x: 5
#:> y: 8

However, you can also specify the argument assigment during function call

myfun (y=8,x=5)

#:> x: 5
#:> y: 8

Function can have default argement value

def myfun(x=1,y=1):  # default argument value is 1
    print ('x:',x)
    print ('y:',y)
    
myfun(5)  # pass only one argument

#:> x: 5
#:> y: 1

5.3.2 List Within Function

Consider a function is an object, its variable (some_list) is immutable and hence its reference won’t change, even data changes

def spam (elem, some_list=[]):
    some_list.append(elem)
    return some_list

print (spam(1))

#:> [1]

print (spam(2))

#:> [1, 2]

print (spam(3))

#:> [1, 2, 3]

5.3.3 Return Statement

def bigger(x,y):
    if (x>y):
        return x
    else:
        return y
    
print (bigger(5,8))

#:> 8

5.3.4 No Return Statement

if no return statement, python return None

def dummy():
    print ('This is a dummy function, return no value')

dummy()

#:> This is a dummy function, return no value

5.3.5 Return Multiple Value

Multiple value is returned as tuple. Use multiple assignment to assign to multiple variable

def minmax(x,y,z):
    return min(x,y,z), max(x,y,z)

a,b = minmax(7,8,9)     # multiple assignment
c   = minmax(7,8,9)     # tuple

print (a,b)

#:> 7 9

print (c)    

#:> (7, 9)

5.3.6 Passing Function as Argument

You can pass a function name as an argument to a function

def myfun(x,y,f):
    f(x,y)

myfun('hello',54,print)

#:> hello 54

5.3.7 Arguments

args is a tuple

def myfun(x,*args):
    print (x)
    print (args)     #tuple
    
myfun(1,2,3,4,5,'abc')

#:> 1
#:> (2, 3, 4, 5, 'abc')

def myfun(x,y,*args):
    print (x)
    print (y)
    print (args)     #tuple
    
myfun(1,2,3)

#:> 1
#:> 2
#:> (3,)

def myfun(x,*args, y=9):
    print (x)
    print (y)
    print (args)     #tuple
    
myfun(1,2,3,4,5)

#:> 1
#:> 9
#:> (2, 3, 4, 5)

def myfun(*args):
    print (args)     #tuple
    
myfun(1,2,3,4,5)

#:> (1, 2, 3, 4, 5)

def myfun(x,y,*args):
    print (x)
    print (y)
    print (args)
    
myfun(1,2)

#:> 1
#:> 2
#:> ()

5.3.8 keyword arguments

kwargs is a dictionary

def foo(**kwargs):
    print(kwargs)
    
foo(a=1,b=2,c=3)

#:> {'a': 1, 'b': 2, 'c': 3}

def foo(x,**kwargs):
    print(x)
    print(kwargs)
    
foo(9,a=1,b=2,c=3)

#:> 9
#:> {'a': 1, 'b': 2, 'c': 3}

foo(9) #empty dictionary

#:> 9
#:> {}

def foo(a,b,c,d=1):
    print(a)
    print(b)
    print(c)
    print(d)
    
foo(**{"a":2,"b":3,"c":4})

#:> 2
#:> 3
#:> 4
#:> 1

5.3.9 Mixing *args, **kwargs

Always put args before kwargs

def foo(x,y=1,**kwargs):
    print (x)
    print (y)
    print (kwargs)
    
foo(1,2,c=3,d=4)

#:> 1
#:> 2
#:> {'c': 3, 'd': 4}

def foo(x,y=2,*args,**kwargs):
    print (x)
    print (y)
    print (args)
    print (kwargs)
    
foo(1,2,3,4,5,c=6,d=7)

#:> 1
#:> 2
#:> (3, 4, 5)
#:> {'c': 6, 'd': 7}