ESC+H : terminal commands

The Jupyter Notebook has two different keyboard input modes. Edit mode allows you to type code/text into a cell and is indicated by a green cell border. Command mode binds the keyboard to notebook level actions and is indicated by a grey cell border with a blue left margin.
In the new IPython cells could have two states: when it has a green selection rectangle around it you can edit what's inside; when it has a grey rectangle around it you edit the cell itself (copy/paste/delete). Enter/Return makes it go green, Esc makes it go grey. When it is gray, 'dd' will delete it.

Terminal warmup

pwd

ls

Some tweaks needed from ipython to jupyter: run, paste, edit

9*54

# Last command results
_

x=_

# Show cell 27 contents
rep 27

9*54

exec _i27

Adavance Python

#Instead of range, use xrange to avoid pre-generate
for i in xrange(2):
    print i;

0
1

for item in L:
    print item

L = ['Tom', 'Henry', 'Harry']

#Looping
print '#Looping'
for item in L:
    print item

#Index
print '#Index'
for i in xrange(len(L)):
    print i, L[i]

#Enumerate
print '#Enumerate in below'
C = enumerate(L)
print C
for i, item in enumerate(L):
    print i, item

#Looping
Tom
Henry
Harry
#Index
0 Tom
1 Henry
2 Harry
#Enumerate in below
<enumerate object at 0x1064229b0>
0 Tom
1 Henry
2 Harry

String List Zip

first_names = ['Giovanna', 'Ryan', 'Jon']
last_names = ['Thron', 'Orban', 'Dinu']

#Loop two lists together
for i in xrange(len(first_names)):
    print first_names[i], last_names[i]

#Zip two lists by tuples
print zip(first_names, last_names)

#izip
from itertools import izip
for first, last in izip(first_names, last_names):
    print first, last

Giovanna Thron
Ryan Orban
Jon Dinu
[('Giovanna', 'Thron'), ('Ryan', 'Orban'), ('Jon', 'Dinu')]
Giovanna Thron
Ryan Orban
Jon Dinu

from itertools import izip, count
for i, first, last in izip(count(), first_names, last_names): 
    print i, first, last

0 Giovanna Thron
1 Ryan Orban
2 Jon Dinu

note to use count() inside izip() function, instead of count.

2D List Comperhension

List of list: Lowest goes first, inside then outside
One list: top to down

#Double loop
L = [[1,2,3],[4,5,6],[7,8,9]]
doubled = []
for row in L:
    row2= []
    for item in row:
        row2.append(item*2)
    doubled.append(row2)
doubled

[[2, 4, 6], [8, 10, 12], [14, 16, 18]]

#List Comprehension
doubled = [[item *2 for item in row]for row in L]
doubled

[[2, 4, 6], [8, 10, 12], [14, 16, 18]]

#Flatten: *Note the order of the loop statements.
flat_double = [item for row in L for item in row]
print flat_double
#or translate to be:
flat_double1=[]
for row in L:
    for item in row:
        flat_double1.append(item)
print flat_double1

[1, 2, 3, 4, 5, 6, 7, 8, 9]
[1, 2, 3, 4, 5, 6, 7, 8, 9]

#If statements as filter
evens = [item for item in flat_double if item%2 ==0]
print evens

[2, 4, 6, 8]
[2, 4, 6, 8]





[2, 4, 6, 8]

# or translated to be:
evens1 = []
for item in flat_double:
    if item%2 == 0:
        evens1.append(item)
print evens1

[2, 4, 6, 8]

#Pure computing, no assignment
[item for item in flat_double if item%2 ==0]

[2, 4, 6, 8]

Generator Comprehension for String

L = ["zack desario", "giovanna thron", "ryan orban", "jonathan dinu"]
M = [item for item in L] #Does not change anything
print 'M = ', M
P = (item.split() for item in L) #List of list by .split().
# Use (), 'P, a gernator, does not give a list, only an object'
print 'P =',P
# Use [], N will be a list.
N = [item.split() for item in L] #List of list by .split().
print 'N = ', N

M =  ['zack desario', 'giovanna thron', 'ryan orban', 'jonathan dinu']
P = <generator object <genexpr> at 0x1063cceb0>
N =  [['zack', 'desario'], ['giovanna', 'thron'], ['ryan', 'orban'], ['jonathan', 'dinu']]

# Use [ ]
for name in [item.split()[0] for item in L]:
    print name

zack
giovanna
ryan
jonathan

# Use ( )
for name in (item.split()[0] for item in L):
    print name

zack
giovanna
ryan
jonathan

Generators so far

use ( ) instead of [ ]
item.split()
use xrange() instead of rang()

Lambda Functions:

Lambda to define unnamed functions to customize sort and use functions like map, filter and reduce. Remember, a lambda expression looks like this: lambda variable: variable expression

L = [(2, 4), (5, 3), (6, 8), (4, 1)]
sorted(L)

[(2, 4), (4, 1), (5, 3), (6, 8)]

L.sort(key=lambda x: x[0])

All things you can do with list comprehensions you can also do with map. It's more "Pythonic" to use list comprehensions, but understanding how to write maps is key for numpy and pandas, modules we will be using heavily.

# Double every element of a list
def double_list(L):
    return map(lambda x: x * 2, L)
double_list(L)

[(2, 4, 2, 4), (5, 3, 5, 3), (6, 8, 6, 8), (4, 1, 4, 1)]

garbled = "IXXX aXXmX aXXXnXoXXXXXtXhXeXXXXrX sXXXXeXcXXXrXeXt mXXeXsXXXsXaXXXXXXgXeX!XX"
message = filter(lambda x: x!="X", garbled)
print message

I am another secret message!

#number 1 to 10 means including 10, so range(1,11)
squares = [x**2 for x in range(1,11)]
print squares
print filter(lambda x: x>=30 and x<=70, squares)

[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
[36, 49, 64]

Lambdas are useful when you need a quick function to do some work for you. If you plan on creating a function you'll use over and over, you're better off using def and giving that function a name.

languages = ["HTML", "JavaScript", "Python", "Ruby"]
print filter(lambda x: x=="Python", languages)

['Python']

Only we don't need to actually give the function a name; it does its work and returns a value without one. That's why the function the lambda creates is an anonymous function. When we pass the lambda to filter, filter uses the lambda to determine what to filter, and the second argument (my_list, which is just the numbers 0 – 15) is the list it does the filtering on.

my_list = range(16)
print filter(lambda x: x % 3 == 0, my_list)

[0, 3, 6, 9, 12, 15]

String and indices

#Stride
str = "ABCDEFGHIJ"
start, end, stride = 1, 6, 2
str[start:end:stride]

'BDF'

# Reverse
garbled = "!XeXgXaXsXsXeXmX XtXeXrXcXeXsX XeXhXtX XmXaX XI"
message=garbled[::-1]
print message
message=message[::2] #Save it back after slicing the string.
print message

IX XaXmX XtXhXeX XsXeXcXrXeXtX XmXeXsXsXaXgXeX!
I am the secret message!

letters = ['A', 'B', 'C', 'D', 'E']
print letters[::-1]

['E', 'D', 'C', 'B', 'A']

# The default starting index is 0.
# The default ending index is the end of the list.
# The default stride is 1.
# Omit Indices
to_five = ['A', 'B', 'C', 'D', 'E'] 
print to_five[3:] # prints ['D', 'E'] 
print to_five[:2] # prints ['A', 'B'] 
print to_five[::2] # print ['A', 'C', 'E']

['D', 'E']
['A', 'B']
['A', 'C', 'E']

cdingding / Codecad_Python_Projects