Summer of code 2017: Python, Pretty printing with pprint in Python

As explained in my Summer of code 2017: Python post I decided to pick up Python

This post is about using pprint to pretty print.


The pprint module provides a capability to “pretty-print” arbitrary Python data structures in a form which can be used as input to the interpreter. The formatted representation keeps objects on a single line if it can, and breaks them onto multiple lines if they don’t fit within the allowed width. Construct PrettyPrinter objects explicitly if you need to adjust the width constraint.

Let's take a look at a dictionary

First we do a regular print

>>> stocks ={
'TGT' :  '51.33', 
'AAPL': '147.48',
'MSFT':  '71.49',
'F'   :  '11.12', 
'INTC':  '34.37'}
>>> print(stocks)
{'TGT': '51.33', 'AAPL': '147.48', 'MSFT': '71.49', 'F': '11.12', 'INTC': '34.37'}

As you can see everything is printed on one line

You can print on multiple lines by using a loop and format

stocks ={
'TGT' :  '51.33', 
'AAPL': '147.48',
'MSFT':  '71.49',
'F'   :  '11.12', 
'INTC':  '34.37'}
>>> for key in stocks:
    print("{key} = {value}".format(key=key, value=stocks[key]))

    
TGT = 51.33
AAPL = 147.48
MSFT = 71.49
F = 11.12
INTC = 34.37

Finally let's take a look at what pprint does

>>> stocks ={
'TGT' :  '51.33', 
'AAPL': '147.48',
'MSFT':  '71.49',
'F'   :  '11.12', 
'INTC':  '34.37'}
>>> from pprint import pprint as pp
>>> pp(stocks)
{'AAPL': '147.48',
 'F': '11.12',
 'INTC': '34.37',
 'MSFT': '71.49',
 'TGT': '51.33'}

As you can see, each key value pair is on one line

What about lists?

A list of integers looks pretty much the same

>>> a =  [ [2],[4], [1]]
>>> print(a)
[[2], [4], [1]]
>>> pp(a)
[[2], [4], [1]]

A list of strings is a different story

>>> l ="SpaceX successfully launches and recovers second Falcon 9 in 48 hours".split()
>>> print(l)
['SpaceX', 'successfully', 'launches', 'and', 'recovers', 'second', 'Falcon', '9',
 'in', '48', 'hours']
>>> pp(l)
['SpaceX',
 'successfully',
 'launches',
 'and',
 'recovers',
 'second',
 'Falcon',
 '9',
 'in',
 '48',
 'hours']
>>> 

As you can see that prints the elements on a separate line

The pprint module also supports some keyword parameters like indent, width, depth, let's take a look at indent

>>> import pprint
>>> l ="SpaceX successfully launches and recovers second Falcon 9 in 48 hours".split()
>>> pp = pprint.PrettyPrinter(indent=6)
>>> 
>>> pp.pprint(l)
[     'SpaceX',
      'successfully',
      'launches',
      'and',
      'recovers',
      'second',
      'Falcon',
      '9',
      'in',
      '48',
      'hours']
>>> 

As you can see the values are moved to the right by 6 spaces

Make sure to look at the examples in the docs online to see what other things pprint supports

 

Summer of code 2017: Python, Day 7 Collections: tuple, str and range

As explained in my Summer of code 2017: Python post I decided to pick up Python

This is officially day 7, today, I looked at Collections in Python, here are my notes

Tuples

 A tuple is a heterogeneous immutable sequence

• A tuple is delimited by parentheses
• Items in a tuple are separated by commas
• Element access in a tuple is done with square brackets and zero-based index t[index]
• To get the number of elements in a tuple, use len(t)
• Iterate over a tuple by using a for loop

Here is an example of what I described above

>>> t = ("Denis", "looks", "at", "tuples", 1, 66.100,5)
>>> len(t)
7
>>> t[2]
'at'
>>> t[6]
5
>>> for item in t:
 print(item)

 
Denis
looks
at
tuples
1
66.1
5
>>> 

• Concatenation of tuples with + operator
• Repetition of tuples with * operator

Here is an example of the  + operator as well as the * operator

>>> t = ("Denis", 1, 66.100)
>>> t + (3,2)
('Denis', 1, 66.1, 3, 2)
>>> t * 5
('Denis', 1, 66.1, 'Denis', 1, 66.1, 'Denis',
 1, 66.1, 'Denis', 1, 66.1, 'Denis', 1, 66.1)
>>> 

Tuples can contain any type of object
You can nest tuples
You access inner elements by using chain square-brackets indexing

>>> t = (("Denis", "looks") , (1,2), (5.1, 6.1))
>>> t[2][1]
6.1
>>> t[0][1]
'looks'
>>> t[0][0]
'Denis'
>>> 

Min and max functions can be used

>>> z = (1,2,4,7,9)
>>> min(z)
1
>>> max(z)
9

You don't need parentheses when creating tuples, you can ommit them

>>> x =1,4,7,9
>>> min(x)
1
>>> max(x)
9
>>> x
(1, 4, 7, 9)

However when printing the tuple to the console, the parentheses are displayed


Swapping
a, b = b, a is the idiomatic Python swap
Here is what it looks like

>>> x = 'ice'
>>> y = 'cream'
>>> x, y = y, x
>>> x
'cream'
>>> y
'ice'
>>> 

Tuple(iterable) constructor to create tuples from iterable series of objects

>>> tuple("abcdefg")
('a', 'b', 'c', 'd', 'e', 'f', 'g')
>>> 

This can be handy to find the min and max character from a string

>>> x = tuple("abcdefgdddzyyyaaa")
>>> min(x)
'a'
>>> max(x)
'z'
>>> 

To test for membership, you can use in and not in

>>> x = tuple("abcdefgdddzyyyaaa")
>>> "z" in(x)
True
>>> "m" in(x)
False
>>> "m" not in(x)
True
>>> "z" not in(x)
False
>>> 

And that's it for tuples

str

I will use str and string interchangeably in this post
a str is an immutable sequence of Unicode characters

len
Len gives you the number of characters in a str

>>> s = "abc"
>>> len(s)
3
>>> s = "  b  "
>>> len(s)
5
>>> 

As you can see, spaces are counted unlike the LEN function is SQL Server where spaces are trimmed from the end and start of a string

You can concatenate strings by using the + operator but just like in other language this is not efficient because it will create a new object

>>> s ="Den"
>>> s += "is"
>>> s
'Denis'
>>> 

What you should do is use join

Here is an example where we concatenate is to the string y

>>> y ="Den"
>>> ''.join([y,'is'])
'Denis'

As you can see Denis is printed to the console

Partition
The partition() method divides a string into three pieces around a separator: prefix, separator, suffix

In the code below, you can see that firstname and lastname have the values we want after we used partition with the separator

firstname, separator, lastname= "Michael:Jackson".partition(':')
>>> firstname
'Michael'
>>> lastname
'Jackson'

Use an underscore as a dummy name for the separator, this is also used by the many Python tools

>>> firstname, _, lastname= "Michael:Jordan".partition(':')
>>> firstname
'Michael'
>>> lastname
'Jordan'
>>> 

Format
Use format() to insert values into strings, replacement fields are delimited by { and }
Here is an example

>>> 
"My name is {0}, {1} {0}".format("Bond", "James")
'My name is Bond, James Bond'
>>> 

Range

A range is an arithmetic progression of integers, you can specify where to start, where to end and what the step is. A range is half-open, start is included but stop is not

Constructor	Arguments	Result
range(6)	stop	0, 1, 2, 3, 4, 5
range(6, 10)	start, stop	6, 7, 8, 9
range(10, 20, 2)	start, stop, step	10, 12, 14, 16, 18

Here is what it looks like in the console, range(5) will hold numbers between 0 and 4

>>> x = range(5)
>>> x
range(0, 5)
>>> for item in x:
 print(item)

 
0
1
2
3
4
>>> 

Here is what it looks like in the console, range(0, 10) will hold numbers between 0 and 9

>>> x = range(0,10)
>>> for item in x:
 print(item)

 
0
1
2
3
4
5
6
7
8
9

Here is what it looks like in the console, range(0, 10, 2) will hold numbers between 0 and 9, but because step 2 was supplied, it will be on the numbers 0,2,4,6 and 8

>>> x = range(0,10,2)
>>> x
range(0, 10, 2)
>>> for item in x:
 print(item)

 
0
2
4
6
8
>>> 

That it is for today..I will continue with collections and I will look at list, dict and set

Summer of code 2017: Python, Day 5 Objects

As explained in my Summer of code 2017: Python post I decided to pick up Python

Today is officially day 5, today, I looked at objects in Python, here are my notes

if you do something like this

x = 1000

Python creates an int object with a value of 1000, x now points to this object with a value of 1000
if you now do this
x = 500

Python will not change the value of the object from 1000 to 500 but will instead create another object with a value of 500 and z will now point to that object. The garbage collector will destroy the object with a value of 1000. This all happens because in Python objects are immutable, they cannot change


If you assign  1000 to x, then assign 500 to y, then assign x to y, both are pointing to the same object. You can prove that by using the id() function

In this example below, you will see that after we assign x to y, bot x and y point to the same object with id 50127440

>>> x = 1000
>>> y = 500
>>> y =x
>>> y
1000
>>> x
1000
>>> id(x)
50127440
>>> id(y)
50127440
>>> 

What if you have two variables and assign the same value?

>>> a = 1
>>> b =1
>>> id(a)
499688544
>>> id(b)
499688544
>>> 

As you can see, those also point to the same object

You can also us is to see if 2 objects are the same, so if you do x is y, you will get back True or False

>>> x = 5
>>> y = 5
>>> x is y
True
>>> 

If you do math against a variable, the id will also change

>>> z = 5
>>> id(z)
499688672
>>> z +=2
>>> id(z)
499688736
>>> 

With list it works like this

if you have a list d [1, 2, 3], now you add list e with the values of list d, now both d and e are [1, 2, 3]. If you now modify the list for e to be [1, 1000, 3],  both  e and d are now [1, 1000, 3]. This is because you modified the list object from [1, 2, 3] to [1, 1000, 3] and both d and e point to this list object

Here is what it looks like in IDLE

>>> d = [1, 2, 3]
>>> d
[1, 2, 3]
>>> e = d
>>> e
[1, 2, 3]
>>> e[1] = 1000
>>> e
[1, 1000, 3]
>>> d
[1, 1000, 3]
>>> e is d
True
>>> 

What will happen if we create 2 lists with the same values by assign the values to each list. Now the values are the same

>>> f = [1, 2]
>>> g = [1, 2]
>>> f == g
True
>>> f is g
False
>>> f == f
True

With integers, both is and  == return true

>>> x = 1
>>> y = 1
>>> x == y
True
>>> x  is y
True
>>> 

The is operator determines equality of identity, == determines equivalence


So even though people call these object variables in Python, these are really named references to objects


I also learned about the dir built-in function

Without arguments, return the list of names in the current local scope. With an argument, attempt to return a list of valid attributes for that object.

The default dir() mechanism behaves differently with different types of objects, as it attempts to produce the most relevant, rather than complete, information:

• If the object is a module object, the list contains the names of the module’s attributes.
• If the object is a type or class object, the list contains the names of its attributes, and recursively of the attributes of its bases.
• Otherwise, the list contains the object’s attributes’ names, the names of its class’s attributes, and recursively of the attributes of its class’s base classes.

So for example if we call dir on the math object, it will return all the functions available

>>> import math
>>> type(math)

>>> dir(math)
['__doc__', '__loader__', '__name__', '__package__', '__spec__', 'acos', 'acosh',
 'asin', 'asinh', 'atan', 'atan2', 'atanh', 'ceil', 'copysign', 'cos', 'cosh', 
'degrees', 'e', 'erf', 'erfc', 'exp', 'expm1', 'fabs', 'factorial', 'floor', 'fmod', 
'frexp', 'fsum', 'gamma', 'gcd', 'hypot', 'inf', 'isclose', 'isfinite', 'isinf', 'isnan', 
'ldexp', 'lgamma', 'log', 'log10', 'log1p', 'log2', 'modf', 'nan', 'pi', 'pow', 'radians', 
'sin', 'sinh', 'sqrt', 'tan', 'tanh', 'tau', 'trunc']
>>> math.pi
3.141592653589793
>>> math.pow(2,4)
16.0
>>> 

So this is a quick way to get all the available methods/functions from a class

Summer of code 2017: Python local help files

As explained in my Summer of code 2017: Python post I decided to pick up Python

I noticed that Python ships with a help file in chm format ( Compiled HTML Help)



Microsoft Compiled HTML Help is a Microsoft proprietary online help format, consisting of a collection of HTML pages, an index and other navigation tools. The files are compressed and deployed in a binary format with the extension .CHM, for Compiled HTML. The format is often used for software documentation.

I haven't used a chm file since SQL Server 2000 within Query Analyzer. I prefer these files over online files for multiple reason

You don't have to be online to access the help file, you can be coding in a cave without connectivity and you can still pull up help

You can bookmark pages you want to get back to over and over again, these will be in the favorites tab

There is an index tab, this is like the back of a book, it is in alphabetical order and you can quickly find stuff

I typed in string, hit enter and saw the following

Then I clicked on method and was presented with the page you see

Do you use the local help file or do you use the online documentation?

Summer of code 2017: Python, Day 2

As explained in my Summer of code 2017: Python post I decided to pick up Python

Today is officially day 2

I decided to do a lunch and learn today and continue with the PluralSight course: Python Fundamentals

The course continued with Strings. Strings are very similar as strings in other languages

Here are some of the notes for myself of what I learned today


You can use single or double quotes with strings

Universal Newlines, you can use "\n" and it will be a newline on all platforms, this is also part of PEP 278

Multi-line strings are created by using triple quotes

For example

>>> x = """fdfdfdf
dfd
fdf
df
dfdf"""
>>> x
'fdfdfdf\ndfd\nfdf\ndf\ndfdf'
>>> 

As you can see, when the console prints the string, you will see the \n escape characters

Here are some of these escape characters

Escape Sequence	Meaning	Notes
\newline	Backslash and newline ignored
\\	Backslash (\)
\'	Single quote (')
\"	Double quote (")
\a	ASCII Bell (BEL)
\b	ASCII Backspace (BS)
\f	ASCII Formfeed (FF)
\n	ASCII Linefeed (LF)
\r	ASCII Carriage Return (CR)
\t	ASCII Horizontal Tab (TAB)
\v	ASCII Vertical Tab (VT)
\ooo	Character with octal value ooo
\xhh	Character with hex value hh

Escape sequences only recognized in string literals are:

Escape Sequence	Meaning	Notes
\N{name}	Character named name in the Unicode database
\uxxxx	Character with 16-bit hex value xxxx
\Uxxxxxxxx	Character with 32-bit hex value xxxxxxxx

More about that here: https://docs.python.org/3/reference/lexical_analysis.html#strings

Formatted String Literals

A formatted string literal or f-string is a string literal that is prefixed with 'f' or 'F'. These strings may contain replacement fields, which are expressions delimited by curly braces {}. While other string literals always have a constant value, formatted strings are really expressions evaluated at run time.

Here is an example

>>> name = "Denis"
>>> f"He said his name is {name!r}."
"He said his name is 'Denis'."
>>> 

Strings are unicode and encoded in UTF-8

After strings, the course continued with bytes, lists, dictionaries and loops

Modularity

This was the next part of this course
Named functions are defned with the def keyword

def function_name(arg1, argn):


For example

>>> def sumvalues(x,y):
    return x + y

>>> sumvalues(4,5)
9
>>> 

If you use a return without a value, the function will return None, but remember that None is not printed from the REPL

If you were to save this function into a file and then import it, it would execute immediately

Python has special attributes that start and end with double underscores, we will look at __main__ and  __name__

'__main__' is the name of the scope in which top-level code executes. A module’s __name__ is set equal to '__main__' when read from standard input, a script, or from an interactive prompt.

A module can discover whether or not it is running in the main scope by checking its own __name__, which allows a common idiom for conditionally executing code in a module when it is run as a script or with python -m but not when it is imported:

Here is an example of that

>>> 
def sumvalues(x,y):
    return x + y

    if __name__ == "__main__":
        sumvalues(x,y)

>>> sumvalues(1,2)
3
>>> 

More here: https://docs.python.org/3/library/__main__.html


I also learned about setting up a main() function

Command line arguments are accessible via sys.argv

This module also covered documenting your code by using docstrings. 

Docstrings are standalone literal strings which are the fist statement
of a function or module

If you have this function

>>> def fib2(n):  # return Fibonacci series up to n
    """Return a list containing the Fibonacci series up to n."""
    result = []
    a, b = 0, 1
    while a < n:
        result.append(a)    # see below
        a, b = b, a+b
    return result

Now if you do a help(fib2) command, you will see the following

>>> help(fib2)
Help on function fib2 in module __main__:

fib2(n)
    Return a list containing the Fibonacci series up to n.

>>> 

I feel I need to spend more time with __main__ and __name__.  

I will do that the next couple of days

Summer of code 2017: Python, Day 1

As explained in my Summer of code 2017: Python post I decided to pick up Python

Today is officially day 1... but I really started yesterday

I decided to start with the PluralSight course: Python Fundamentals

This course is presented by  Austin Bingham and Robert Smallshire

This is the description for that course

Python Fundamentals gets you started with Python, a dynamic language popular for web development, big data, science, and scripting. What’s so great about Python? Python is powerful. The Python language is expressive and productive, it comes with a great standard library, and it’s the center of a huge universe of wonderful third-party libraries. With Python you can build everything from simple scripts to complex applications, you can do it quickly, and you can do it with fewer lines of code than you might think possible. But for many people those reasons take back-seat to something more important: Python is fun! Python’s readable style, quick edit-and-run development cycle, and “batteries included” philosophy mean that you can sit down and enjoy writing code rather than fighting compilers and thorny syntax. As your experiments become prototypes and your prototypes become products, Python makes the experience of writing software not just easier but truly enjoyable. In the words of Randall Munroe, "Come join us! Programming is fun again!"

Long integers

Python supports really long integers, most languages I worked with support up to 64 bit integers

In Python you can store 2 to the power of 900 in an integer without a problem

That looks like this in scientific notation

8.452712498170644e+270

Or if you were to print this out as an integer

8452712498170643941637436558664265704301557216577944354047371344426782440907597751590676094202515006314790319892114058862117560952042968596008623655407033230534186943984081346699704282822823056848387726531379014466368452684024987821414350380272583623832617294363807973376

That is 271 digits

Here is what it looks like in the console

>>> x = math.pow(2,900)
>>> print ( int(x))
84527124981706439416374365586642657043015572
16577944354047371344426782440907597751590676
09420251500631479031989211405886211756095204
29685960086236554070332305341869439840813466
99704282822823056848387726531379014466368452
68402498782141435038027258362383261729436380
7973376
>>> print ( len(str(x)))
22
>>> print ( len(str(int(x))))
271
>>> 

Python Enhancement Proposal (PEP)

Python's development is conducted largely through the Python Enhancement Proposal (PEP) process. The PEP process is the primary mechanism for proposing major new features, for collecting community input on an issue, and for documenting the design decisions that have gone into Python.

And index with all the PEPs can be found here: https://www.python.org/dev/peps/

PEP number 8 Style Guide for Python Code is an important one, all Python developers should keep that in mind. In this PEP you will see that you should use spaces not tabs for indentation, You should use 4 spaces per indentation level.


Zen of Python

This is another PEP, the Zen of Python is PEP number 20

The Zen of Python is a collection of 20 software principles that influences the design of Python Programming Language, 19 of these are written down, you can see them by entering the statement import this in the Python interpreter


>>> import this
The Zen of Python, by Tim Peters

Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.
Special cases aren't special enough to break the rules.
Although practicality beats purity.
Errors should never pass silently.
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
There should be one-- and preferably only one --obvious way to do it.
Although that way may not be obvious at first unless you're Dutch.
Now is better than never.
Although never is often better than *right* now.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.
Namespaces are one honking great idea -- let's do more of those!
>>>

That output is the Zen of Python

None

The equivalent of NULL in languages like c#, Java or SQL Server in Python is None

If you assign the None value to a variable and then tried to print it, you won't get anything back

You can however check if a variable has no value by checking for None

>>> y = None

>>> y

>>> 

if y == None:

    print("is none")

else:

    print("is none")

    

is none

I also messed around and struggled to install PyGame, at the end it was pretty simple, you can read that here:  Installing Pygame on windows

Installing Pygame on windows

As explained in my Summer of code 2017: Python post I decided to pick up Python. As explained in that post my son wants to do some game development. with Python you can use Pygame to do game development.

My first attempt to install Pygame didn't end well, the instructions I found were to were to download the pygame wheel file, rename the .whl file to .zip. After that extracting the files into a folder. Then you had to move the header files into the \Python36\include folder. Another thing I had to do was moving the pygame folder and the pygame-1.9.3.dist-info folder into the \Python36\Lib\site-packages folder

After that was done, I got some strange errors, something about init() missing (AttributeError: module 'pygame' has no attribute 'init')


Another option was to use pip

I tried that

C:\Users\dgobo>pip install pygame
Collecting pygame
  Downloading pygame-1.9.3-cp36-cp36m-win_amd64.whl (4.2MB)
    100% |████████████████████████████████| 4.2MB 234kB/s
Installing collected packages: pygame
Successfully installed pygame-1.9.3

I still had an error after this was done

I noticed that pip installed Pygame into the following folder

\anaconda3\lib\site-packages


Hmmm... what is anaconda and why did pip install Pygame there?

I then navigated to the Python directory, instead of pip install pygame I did python -m pip install pygame

C:\Python36>python -m pip install pygame
Collecting pygame
  Using cached pygame-1.9.3-cp36-cp36m-win_amd64.whl
Installing collected packages: pygame
Successfully installed pygame-1.9.3


That did it, after that ran, I had no errors anymore

So all you have to do is..run pip from python, not by itself

Hopefully this will help someone if they run into this issue