How to Update All Packages in Anaconda

To update all packages in Anaconda to the latest version, execute the following command:

conda update --all

Extract Initials from Names using Python

>>> name = "Rizauddin Saian"
>>> ' '.join([n[0] + "." for n in name.split()])
'R. S.'

[nltk_data] Error loading all: HTTP Error 401: Authorization Required

If you get the following error, when downloading the corpus for NLTK,

[nltk_data] Error loading all: HTTP Error 401: Authorization Required

you need to update the current data server setting in "/usr/lib/python2.7/dist-packages/nltk/downloader.py" file on line 370 from

DEFAULT_URL = 'http://nltk.googlecode.com/svn/trunk/nltk_data/index.xml'

to

DEFAULT_URL = "http://nltk.github.com/nltk_data/"

Integrate Vim and IPython in Windows

Ipython and Vim is a great combination that make an IDE for Python.



By default, the IPython will use Windows default editor (Notepad), when %edit command is invoked.

To make Vim as the default editor, please follow the following steps:


Step 1.
Open file ipythonrc.ini which is located at “C:Usersyour username_ipython” in Windows 7 with any editor.


Step 2.
Search for line “editor 0”.

Step 3.
Replace that line to

editor vim

for Vim, or,

editor gvim –f

if  you prefer to use gVim.


Step 4.
Restart IPython and type %edit to start Vim.

Python: Swapping the keys and values of a dictionary

A function to swap the keys and immutable values of a dictionary.

def swap_dict(a_dict):
    return {val:key for key, val in a_dict.items()}

Example of usage:

>>> print(swap_dict({1: 'a', 2: 'b', 3: 'c'}))
{'a': 1, 'c': 3, 'b': 2}

My VIM .vimrc file for working with Python

Here is the VIM .vimrc file that I use to work with Python.

syntax on
set nu
set ts=4
set sw=4
set sts=4
set autoindent
set smartindent
set expandtab
set smarttab

It will

1. Display the line number.


2. Set tab stop to 4.


3. Enable you to use < and > to indent or unindent a block in visual mode.


4. Insert spaces instead of tab, when pressing the tab button.

Python: How to convert a dictionary into a list of key-value

Using the list() function, we can convert a dictionary into a list of key-value tuple.

>>> x = {'a':1, 'b':2}
>>> x
{'a': 1, 'b': 2}
>>> y = list(x.items())
>>> y
[('a', 1), ('b', 2)

To convert back into dictionary, use the dict() function.

>>> z = dict(y)
>>> z
{'a': 1, 'b': 2}

Python: Remove items from a list that occur in another list

Suppose that you have two list x and y. How to remove items from list x that occur in list y?

Method 1

>>> x = [1, 2, 3, 4, 5, 6, 7, 8]
>>> y = [4, 7, 9]
>>> list(set(x) - set(y))
[1, 2, 3, 5, 6, 8]

Method 2

>>> x = [1, 2, 3, 4, 5, 6, 7, 8]
>>> y = [4, 7, 9]
>>> [i for i in x if i not in y]
[1, 2, 3, 5, 6, 8]

I have presented two methods for removing items from list x that occur in list y. If you have better method, please leave a comment.

Python interactive help mode

Python provides an interactive help mode inside the interactive Python interpreter.

This tutorial provides some basic on how to use the help mode.

Enter the help mode

To use it, start the Python interpreter (or, IDLE), and then type help() and press Enter to start the interactive help mode.

Quit the help mode

To exit the help mode, type quit and press Enter.

List of Python keywords

To get a list of available keywords in Python, type keywords and press Enter.

To get help on certain keyword just type the keyword and press enter.

List of available modules

To get a list of available modules in Python, type module and press Enter.

To get help on certain module just type the module name and press enter.

List of available topics

The topics command gives a list of topics regarding Python programming language.

To get a list of available topics, type topics and press Enter.

To get help on certain topic, just type the topic name and press enter.

Count the number of occurences using Counter() in Python

Counter is an object of collections module, and it is a dict subclass for counting hashable objects, in Python 3.

To count the number of elements occurrences in a list

>>> from collections import Counter
>>> z = ['blue', 'red', 'blue', 'yellow', 'blue', 'red']
>>> Counter(z)
Counter({'blue': 3, 'red': 2, 'yellow': 1})

Count the number of alphabet occurrences in a text

>>> from collections import Counter
>>> Counter("This is a test")
Counter({' ': 3, 's': 3, 'i': 2, 't': 2, 'a': 1, 'e': 1, 'h': 1, 'T': 1})

To find the n most common words in a text

n is the number of most common words to find

Counter(the_text).most_common(3)

For more information, read The Python Standard Library

How to list out Python reserved words

To list out the Python reserved words, just enter the following lines into the Python interpreter.

>>> import keyword
>>> print(keyword.kwlist)

['False', 'None', 'True', 'and', 'as', 'assert', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']

Python Reserved Words

Count the number of words using Python

This article represents a way to count the number of words, the number of unique words, and the number of each word occurrences in a text file.

1. Read the text file.
   text = open("filename.txt").read()
2. Replace non-alphanumeric characters as a whitespace.
   import re text = re.sub('[^w&^d]', ' ', text)
3. Change all characters to lowercase.
   text = text.lower()
4. Split words into a list.
   text = text.split()
5. Display the number for words in the text file.
   len(text)
6. Display the number of unique words in the text file.
   len(set(text))
7. Display the number of occurrences for each word.
   from collections import defaultdict
   wordsCount = defaultdict(int)
   for word in text:
       wordsCount[word] += 1
       for word, num in wordsCount.items():
           print(word, num)

How to choose a random item from a sequence in Python

To choose a random item from a list, use random.choice().

Here is an example.

>>> items = ['Proton', 'Honda', 'Toyota', 'Nissan']
>>> random.choice(items)
'Nissan'
>>> random.choice(items)
'Proton'
>>> random.choice(items)
'Toyota'

Another example of usage is to choose a random file from a directory.

>>> random.choice(os.listdir("C:"))
'ubuntu'
>>> random.choice(os.listdir("C:"))
'tex4ht'

How to run Python inside vim

To run the current open Python program in vim, type:

:!python %

How to store functions in a dictionary in Python

This example uses a dictionary to store functions.

To call the function, use the dictionary key.

>>> f = {'plus_all':sum, 'find_max':max}
>>> f['find_max'](1,4,5,3,2,6)
6
>>> f['plus_all'](range(10))
45

The intersection of two Python lists using Set

Set is unordered unique collection of objects.

We can use Set to find the intersection of two lists/tuples.

Suppose that we have two lists.

>>> x = [1, 2, 3, 4, 5]
>>> y = [2, 6, 7, 3]

To find the intersection of the two lists, first change both x and y to the Set type, then use the intersection method (&).

>>> set(x) & set(y)
{2, 3}

If we need the output in list type, apply the list command, to the output.

>>> list(set(x) & set(y))
[2, 3]

How to sort a Python tuple

Python tuple is immutable. Therefore, it cannot be changed.

To sort a Python tuple, we can create a new list using sorted() method.

If we still need it as a tuple, just apply tuple() to the new list.

>>> z = (1, 4, 3, 7, 2, 12, -3, 3)
>>> sorted_z = tuple(sorted(z))
>>> sorted_z
(-3, 1, 2, 3, 3, 4, 7, 12)

How to sort a Python list

Suppose that you have a Python list,

[1, 4, 3, 7, 2, 12, -3, 3]

that needed to be sorted.

The list can be sorted by directly applying the sort() method to the list, and indirectly by using the sorted().

Using sort()

The list will be sorted and the list will now become the new sorted list.

>>> y = [1, 4, 3, 7, 2, 12, -3, 3]
>>> y.sort()
>>> y
[-3, 1, 2, 3, 3, 4, 7, 12]

Using sorted()

The list will be sorted as a new list.

We can create a new sorted list, and the original remains.

>>> y = [1, 4, 3, 7, 2, 12, -3, 3]
>>> sorted(y)
[-3, 1, 2, 3, 3, 4, 7, 12]
>>> y
[1, 4, 3, 7, 2, 12, -3, 3]

How to sum the values of a Python dictionary

Suppose that we have a Python dictionary,

x = {'a': 3, 'b': 2, 'c':7}

and, we want to add the values i.e. 3 + 2 + 7 = 12.

Here are the three ways to add the values.

Using list comprehension

>>> x = {'a': 3, 'b': 2, 'c':7}
>>> sum([i for i in x.values()])
12

Using for loop I

>>> x = {'a': 34, 'b': 2, 'c':7}
>>> total = 0
>>> for i in x.values():
total += i

Using for loop II

>>> x = {'a': 34, 'b': 2, 'c':7}
>>> total = 0
>>> for key in x.keys():
total += x[key]

Convert Strings to Integers/Floats in Python

Strings to integer

To convert a string to an integer:

>>> x = '1234'
>>> int(x)
1234

Strings to float

To convert a string to float:

>>> x = '1234'
>>> float(x)
1234.0

>>> y = '1234.678'
>>> float(y)
1234.6780000000001

but, convertion of '1234.678' to integer using int() will gives an error.

>>> int(y)
Traceback (most recent call last):
File "<pyshell#4>", line 1, in <module>
int(y)
ValueError: invalid literal for int() with base 10: '1234.678'

A workaround is by first converting to float, then to integer:

>>> y = '1234.678'
>>> int(float(y))
1234

List/tuple of strings to list of integers

1. Using list comprehension
   >>> x = ['07', '11', '13', '14', '28']
   >>> [int(i) for i in x]
   [7, 11, 13, 14, 28]
2. Using map
   >>> x = ['07', '11', '13', '14', '28']
   >>> list(map(int, x))
   [7, 11, 13, 14, 28]
   Mix of integers and floats
   >>> x = ['7.424124', '11', '13.423', '14.53453656', '28.2']
   >>> list(map(int, map(float, x)))
   [7, 11, 13, 14, 28]

List/tuple of strings to list of floats

1. Using list comprehension
   >>> x = ['7.424124', '1', '13.423', '14.53453656', '28.2']
   >>> [float(i) for i in x]
   [7.4241239999999999, 1.0, 13.423,
   14.534536559999999, 28.199999999999999]
   
2. Using map
   >>> x = ['7.424124', '1', '13.423', '14.53453656', '28.2']
   >>> list(map(float, x))
   [7.4241239999999999, 1.0, 13.423,
   14.534536559999999, 28.199999999999999]