Introduction to Python (Part 1)¶

IPython kernel is polyglot¶

In [1]:

%%bash

echo $PATH

/opt/conda/bin:/opt/conda/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

In [3]:

%load_ext rpy2.ipython

In [4]:

%%R

1:10

[1]  1  2  3  4  5  6  7  8  9 10

In [7]:

%%R -o iris

head(iris)

Sepal.Length Sepal.Width Petal.Length Petal.Width Species
        5.1         3.5          1.4         0.2  setosa
        4.9         3.0          1.4         0.2  setosa
        4.7         3.2          1.3         0.2  setosa
        4.6         3.1          1.5         0.2  setosa
        5.0         3.6          1.4         0.2  setosa
        5.4         3.9          1.7         0.4  setosa

In [8]:

iris.head()

Out[8]:

	Sepal.Length	Sepal.Width	Petal.Length	Petal.Width	Species
1	5.1	3.5	1.4	0.2	setosa
2	4.9	3.0	1.4	0.2	setosa
3	4.7	3.2	1.3	0.2	setosa
4	4.6	3.1	1.5	0.2	setosa
5	5.0	3.6	1.4	0.2	setosa

Operators¶

In [9]:

2 + 3

Out[9]:

In [10]:

2 * 3

Out[10]:

In [11]:

2 ** 3

Out[11]:

In [12]:

2 / 3

Out[12]:

0.6666666666666666

In [14]:

2 // 3

Out[14]:

In [15]:

7  % 2

Out[15]:

In [16]:

2 < 3

Out[16]:

True

In [17]:

2 <= 3

Out[17]:

True

In [18]:

2 == 3

Out[18]:

False

In [19]:

2 != 3

Out[19]:

True

In [22]:

(2 < 3) and (3 < 2)

Out[22]:

False

In [23]:

(2 < 3) or (3 < 2)

Out[23]:

True

Strings¶

In [24]:

'hello world'

Out[24]:

'hello world'

In [25]:

"hello world"

Out[25]:

'hello world'

In [26]:

'''
One
Two
Three
'''

Out[26]:

'\nOne\nTwo\nThree\n'

In [27]:

"""One
Two
Three"""

Out[27]:

'One\nTwo\nThree'

In [28]:

print("""One
Two
Three""")

One
Two
Three

In [29]:

s = 'hello world'

In [30]:

s[:3]

Out[30]:

'hel'

In [31]:

s[3:]

Out[31]:

'lo world'

In [32]:

s[-3:]

Out[32]:

'rld'

Lists¶

In [33]:

xs = [1,2,3,4,5]

In [34]:

xs

Out[34]:

[1, 2, 3, 4, 5]

In [35]:

xs[:3]

Out[35]:

[1, 2, 3]

In [36]:

xs[3:]

Out[36]:

[4, 5]

In [38]:

ys = [1,2,3,'hello world', [8,9,10]]

In [39]:

ys

Out[39]:

[1, 2, 3, 'hello world', [8, 9, 10]]

In [40]:

ys[-1][1]

Out[40]:

In [41]:

ys[-1][1] = 'X'

In [42]:

ys

Out[42]:

[1, 2, 3, 'hello world', [8, 'X', 10]]

Mutability and immutability¶

In [43]:

Out[43]:

'hello world'

In [44]:

s[2] = 'x'


TypeErrorTraceback (most recent call last)
<ipython-input-44-a3feb2c3ba3f> in <module>()
----> 1 s[2] = 'x'

TypeError: 'str' object does not support item assignment

Tuples¶

In [45]:

zs = (1,2,3,4,'hello world')

In [46]:

zs

Out[46]:

(1, 2, 3, 4, 'hello world')

In [47]:

zs[2] = 'x'


TypeErrorTraceback (most recent call last)
<ipython-input-47-9ccfac1c6e9c> in <module>()
----> 1 zs[2] = 'x'

TypeError: 'tuple' object does not support item assignment

In [48]:

zs = 1, 2, 3, 4, 'hello world'

In [49]:

zs

Out[49]:

(1, 2, 3, 4, 'hello world')

Dictionaries¶

In [53]:

a = {
    'a': 1,
    'b': 2,
    'c': 3,
    'hello world': 4,
    (1,2,3): 5
}

In [51]:

Out[51]:

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

In [52]:

a['b']

Out[52]:

In [54]:

a[(1,2,3)]

Out[54]:

In [55]:

a['hello world']

Out[55]:

In [56]:

xs = [1,1,1,2,3,3,4]

In [57]:

xs

Out[57]:

[1, 1, 1, 2, 3, 3, 4]

Sets¶

In [58]:

s1 = set(xs)

In [59]:

s1

Out[59]:

{1, 2, 3, 4}

Multiset, bag, counter¶

In [60]:

from collections import Counter

In [61]:

c = Counter(xs)

In [62]:

Out[62]:

Counter({1: 3, 2: 1, 3: 2, 4: 1})

Packages and the import statement¶

In [63]:

import collections

In [64]:

collections.Counter([1,1,2])

Out[64]:

Counter({1: 2, 2: 1})

In [65]:

import collections as coll

In [66]:

coll.Counter([1,1,1,2])

Out[66]:

Counter({1: 3, 2: 1})

In [67]:

import numpy as np

In [69]:

np.linspace(1, 10, 20)

Out[69]:

array([  1.        ,   1.47368421,   1.94736842,   2.42105263,
         2.89473684,   3.36842105,   3.84210526,   4.31578947,
         4.78947368,   5.26315789,   5.73684211,   6.21052632,
         6.68421053,   7.15789474,   7.63157895,   8.10526316,
         8.57894737,   9.05263158,   9.52631579,  10.        ])

Built-in functions¶

In [70]:

s = 'hello world'

In [71]:

len(s)

Out[71]:

In [72]:

len([1,2,3])

Out[72]:

In [73]:

len([1,2,[3,4]])

Out[73]:

In [74]:

ord('a')

Out[74]:

In [75]:

chr(97)

Out[75]:

'a'

In [76]:

for char in 'abc':
    print(ord(char))

97
98
99

In [77]:

xs = [1,2,3]
n = len(xs)
for i in range(n):
    print(i, xs[i])

0 1
1 2
2 3

In [80]:

range(5)

Out[80]:

range(0, 5)

In [79]:

list(range(5))

Out[79]:

[0, 1, 2, 3, 4]

String indexing¶

In [81]:

Out[81]:

'hello world'

In [82]:

s[3:5]

Out[82]:

'lo'

In [83]:

s[::2]

Out[83]:

'hlowrd'

In [84]:

s[1::2]

Out[84]:

'el ol'

In [85]:

s[::-1]

Out[85]:

'dlrow olleh'

In [86]:

s[::-2]

Out[86]:

'drwolh'

In [88]:

list(reversed(s))

Out[88]:

['d', 'l', 'r', 'o', 'w', ' ', 'o', 'l', 'l', 'e', 'h']

In [89]:

help(s)

No Python documentation found for 'hello world'.
Use help() to get the interactive help utility.
Use help(str) for help on the str class.

String methods¶

In [90]:

s.count('o')

Out[90]:

In [92]:

dna = 'AATTAGAGGACCAATTT'

In [94]:

dna.count('C') + dna.count('G')

Out[94]:

In [95]:

s.upper()

Out[95]:

'HELLO WORLD'

In [96]:

import string

In [97]:

string.ascii_letters

Out[97]:

'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'

In [98]:

string.ascii_lowercase

Out[98]:

'abcdefghijklmnopqrstuvwxyz'

In [99]:

string.ascii_uppercase

Out[99]:

'ABCDEFGHIJKLMNOPQRSTUVWXYZ'

In [100]:

string.punctuation

Out[100]:

'!"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}~'

String translation¶

In [101]:

table = str.maketrans(string.ascii_lowercase, string.ascii_uppercase)

In [102]:

Out[102]:

'hello world'

In [103]:

s.translate(table)

Out[103]:

'HELLO WORLD'

In [104]:

table = str.maketrans('', '', 'aeiou')

In [105]:

s.translate(table)

Out[105]:

'hll wrld'

Joining and splitting strings¶

In [106]:

s.split()

Out[106]:

['hello', 'world']

In [107]:

' '.join(s.split())

Out[107]:

'hello world'

In [108]:

'-'.join(s.split())

Out[108]:

'hello-world'

In [109]:

'+@+'.join(['one', 'two', 'three'])

Out[109]:

'one+@+two+@+three'

In [110]:

Out[110]:

'hello world'

Replacing, concatenation and stripping¶

In [113]:

s = s.replace('hello', 'goodbye')

In [115]:

Out[115]:

'goodbye world'

In [116]:

Out[116]:

'goodbye world'

In [117]:

s + ' tomorrow'

Out[117]:

'goodbye world tomorrow'

In [122]:

s = '\t\t' + s + '\n\n'

In [123]:

Out[123]:

'\t\tgoodbye world\n\n\n\n'

In [124]:

print(s)

                goodbye world

In [125]:

print(s.strip())

goodbye world

Numpy arrays¶

In [126]:

import numpy as np

In [127]:

xs = np.arange(10)

In [128]:

xs

Out[128]:

array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])

In [129]:

xs ** 2

Out[129]:

array([ 0,  1,  4,  9, 16, 25, 36, 49, 64, 81])

In [131]:

xs = np.reshape(xs, (2,5))

In [132]:

xs

Out[132]:

array([[0, 1, 2, 3, 4],
       [5, 6, 7, 8, 9]])

In [133]:

np.array([3,6,8])

Out[133]:

array([3, 6, 8])

In [134]:

xs = [1,2,3]

In [135]:

xs + 3


TypeErrorTraceback (most recent call last)
<ipython-input-135-7efca7633ad0> in <module>()
----> 1 xs + 3

TypeError: can only concatenate list (not "int") to list

In [136]:

xs = np.array([1,2,3])

In [137]:

xs + 3

Out[137]:

array([4, 5, 6])

Custom functions¶

In [139]:

def add(a, b):
    """Add stuff.

    a - something that can be addded
    b - something that can be added

    Returns a + b
    """
    ans = a + b
    return ans

In [140]:

help(add)

Help on function add in module __main__:

add(a, b)
    Add stuff.

    a - something that can be addded
    b - something that can be added

    Returns a + b

In [141]:

x = 2
y = 3
add(x, y)

Out[141]:

In [142]:

add([1,23], [6,7,8])

Out[142]:

[1, 23, 6, 7, 8]

In [ ]:

Introduction to Python (Part 1)¶

IPython kernel is polyglot¶

Operators¶

Strings¶

Lists¶

Mutability and immutability¶

Tuples¶

Dictionaries¶

Sets¶

Multiset, bag, counter¶

Packages and the import statement¶

Built-in functions¶

String indexing¶

String methods¶

String translation¶

Joining and splitting strings¶

Replacing, concatenation and stripping¶

Numpy arrays¶

Custom functions¶

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