[Tutor] getting unknown results

[DL Neil]

On 24/04/20 7:52 PM, shubham sinha wrote:
> The format_address function separates out parts of the address string into
> new strings: house_number and street_name, and returns: "house number X on
> street named Y".
>   The format of the input string is: numeric house number, followed by the
> street name which may contain numbers, but never by themselves, and could
> be several words long.
> For example, "123 Main Street", "1001 1st Ave", or "55 North Center Drive".
> 
> my code:
> def format_address(address_string):
>    # Declare variables
>      number = []
>      place = []
>    # Separate the address string into parts
>      split_string = address_string.split()
>    # Traverse through the address parts
>      for i in range(0, len(split_string)):
>      # Determine if the address part is the
>      # house number or part of the street name
>          if split_string[i].isnumeric():
>    # Does anything else need to be done
>    # before returning the result?
>              number.append(split_string[i])
>          return place.append(split_string[i])
>    # Return the formatted string
>      place = " ".join(place)
>      return "house number {number} on street named {place}".format(number
> ,place = " ".join(place) )
> 
> print(format_address("123 Main Street"))
> # Should print: "house number 123 on street named Main Street"
> 
> print(format_address("1001 1st Ave"))
> # Should print: "house number 1001 on street named 1st Ave"
> 
> print(format_address("55 North Center Drive"))
> # Should print "house number 55 on street named North Center Drive"
> 
> 
> my output:
> 
> None
> None
> None
> 
> 
> I am getting result "none" instead of expected result.
> 
> Please help me through this.

Well done! You seem to have the necessary ingredients. The challenge is 
to look at the detail of Python...


Firstly, a really good way to learn and experiment with Python features 
which are new-learning is the REPL. Fire-up Python from the 
command-line, and then you can type-in individual statements and have 
them resolve immediately.

For example, to verify that code does what you expect, instead of:

	split_string = address_string.split()

use some sample-data and type the following directly into 'Python':

	"123 Main Street".split()

Is the result exactly as you expected? (hope-so, but if not, you've 
saved yourself some time and frustration!)

So, that's a program-design technique. How about debugging at 
execution-time?

May I suggest copy-pasting this code into a tool such as 
http://www.pythontutor.com/ which will illustrate how the computer 
executes code line-by-line? (as do some editor/IDE packages)

Rightly, or wrongly, the impression gained from this code is that a 
couple of functions work differently from the way you seem to expect.

One particular problem is that every time the code finds a numeric value 
within the input, the code-line:

         return place.append(split_string[i])

is returning None (as you noted). Why is the answer being appended to a 
list? Should there be two separate statements, if the list is to be 
returned (ie after being appended)?

- both of the above techniques will illustrate such matters.


You seem to have used other programming languages. Python has a much 
(much, much...) easier way of handling loops by completely dropping 
'pointers'. Instead of:

 >      split_string = address_string.split()
 >    # Traverse through the address parts
 >      for i in range(0, len(split_string)):
 >      # Determine if the address part is the
 >      # house number or part of the street name
 >          if split_string[i].isnumeric():

try:

	for token in address_string.split():
		if token.isnumeric():
			...

What happens here is that the address is split into "tokens" and the 
for-loop enables consideration of each token in-turn. So much easier!


For toy-problems like this and whilst you are learning, it's important 
to realise that we cannot 'see' what the computer is doing (apart from 
the illustrative-tool(s) mentioned earlier). Another common technique is 
to add 'debug print' statements to show what is happening, eg what 
exactly is the value called "token" 'this time' through the loop? From:

	for token in address_string.split():
		if token.isnumeric():

try:

	for token in address_string.split():
		print( token, token.isnumeric() )	# this is it!
		if token.isnumeric():

Thus the print() provides a 'window' into the computer, showing you at 
every cycle of the loop, the token (string) it is considering and 
whether/not that is a numeric value (boolean)!

They are called "debug print" because they are only for fault-finding 
and you will take them out before handing-in the assignment (or putting 
code into 'production')!
NB there are other ways of doing this, but debug-print is the easiest 
for beginners to learn/add to practical exercises.


Enough?
Why don't you try that much, and see how things improve - then revert if 
other questions arise...
-- 
Regards =dn