[Tutor] Fwd: Beginner struggling with python.

[Leam Hall]

Hey Jack, the email list strops off images, attachments, etc.

Here's an example, using the python interpreter itself:

# Calling the interpreter on a Linux box.
[leam at shaphan ~]$ python
Python 3.11.3 (main, May 24 2023, 00:00:00) [GCC 12.3.1 20230508 (Red Hat 12.3.1-1)] on linux
Type "help", "copyright", "credits" or "license" for more information.

# Create the string
>>> f = 'fred'

# Look at the string with upper(). This does NOT change the string!
>>> f.upper()
'FRED'

# Verify the string is unchanged
>>> f
'fred'

# Set another variable with the uppercase string
>>> F = f.upper()
>>> F
'FRED'


Python is easy to learn and fun to use. You'll progress pretty fast.

Leam



On 6/23/23 02:22, Jack Simpson wrote:
> ---------- Forwarded message ---------
> From: Jack Simpson <simpsonrmz41 at gmail.com>
> Date: Fri, 23 Jun 2023 at 1:58 pm
> Subject: Re: [Tutor] Beginner struggling with python.
> To: dn <PythonList at danceswithmice.info>
> 
> 
> I tried to use the string.upper() and it returned this syntax error. I also
> tried def upper() and upper(). I also tried underscores and spaces within
> the string in the parenthesis which produced a similar result but the issue
> was with the  code within the string. I am on a work computer using an
> interpreter so please forgive the photos from my phone.
> 
> On Fri, 23 Jun 2023 at 12:51 pm, dn via Tutor <tutor at python.org> wrote:
> 
>> On 23/06/2023 12.07, Alan Gauld via Tutor wrote:
>>> On 22/06/2023 22:45, Jack Simpson wrote:
>> ...
>>
>>>> nicely until we got on to return values and defining functions. Are
>>>> particular functions built into python such as def convert( etc.
>>
>> Yes, Python offers various built-in functions as well as the opportunity
>> to write your own "custom functions".
>>
>> The 'built-ins' include len( string ) which will return the number of
>> characters in the string - or number of elements in a "collection" when
>> used with a list or similar.
>>
>> There are also 'functions' which are part of a data-type (class).
>> Sticking with strings for the moment: string.upper() will ensure each
>> character in that string is converted (where necessary) into
>> upper-case/capital-letters. In Python, we use the term "everything is an
>> object". So, this function is actually a "method" of the str[ing]
>> type/class. There is an important difference between a function and a
>> method - a method works on the value to which is is attached, eg
>> "string" in this case, whereas a function works independently of any
>> specific instance. (see "arguments" and "result" below - but this
>> distinction is a bit curly for a beginner) You can tell which you're
>> dealing-with, by the 'dotted-notation'.
>>
>> Then there are the functions you can write yourself, as @Alan has
>> described.
>>
>>
>> Noting that functions 'take in' certain (optional) values and return a
>> result, the general form is:
>>
>> def name( arguments ):
>>       # computation
>>       return result
>>
>> The "name" should be a meaningful description of the "computation", ie
>> the purpose of the function.
>>
>> The "arguments" (zero or more) will be a comma-separated list of
>> identifiers which are inputs to the function. In @Alan's example, 7, to
>> produce the seven times-table or 9 when your math is better than mine...
>>
>> The "computation" can be anything which Python will do for you.
>> Sometimes we use a function to attend to a sub-problem within the wider
>> application, ie produces a neatly labelled-result. Another use for
>> functions is when we repeat the same "computation" repeatedly, and
>> perhaps from different points in the application.
>>
>> The "result" seems self explanatory. Every function returns a "result".
>> If there is a return-statement, that will compute a value. If not, the
>> return-value is None. The wording in the singular-form is slightly
>> mis-leading. If appropriate, a function can return a collection of
>> values, eg a tuple or a list - however it is still only one "collection"!
>>
>>
>> We don't have to def-ine built-in functions (or those which are
>> import-ed from a library).
>>
>>
>> The "name( arguments )" and "return result" components are often called
>> the "signature" of the function. Basically, the function says: if you
>> give me this, I'll give you that by-return. Hah! The "signature" is an
>> interface which sets-out all the 'rules' for what you can do with the
>> function - remember the len() example (above), its signature allows us
>> to apply it to a string or a list (or other "collection"). Flexibility!
>> ("polymorphism").
>>
>> The "signature" also advises what to expect as a result: OK the 'length'
>> part is right there in the function-name, but the signature tells us
>> that the return-value will be an integer. Again, not much of a surprise
>> given that we are expecting a number, and it is hard to have a string
>> with a negative-number of characters or indeed part of a character.
>> However, some functions are less obvious and thus the signature is the
>> means of ensuring that we use the function for the purpose and in the
>> manner its author intended.
>>
>> In the Python REPL try: help( function_name )
>> Web.Ref: https://docs.python.org/3/library/functions.html#len
>>
>>
>> Using a function is termed "calling a function". As above, this can look
>> like:
>>
>> number_of_characters = len( string )
>> or
>> seventh_times_table = times_table( 7 )
>>
>> The general form here is:
>>
>> identifier = function_name( parameters )
>>
>> The "signature" is also generalised, but is at-least specific to that
>> particular function.
>>
>> Do we need to document that "function_name" has to correspond to a
>> def-statement (either one of our own, or one built-in and provided to us)?
>>
>> The optional parameters must be provided if the function/signature
>> demands. Some may be required. Others may be optional. There is a
>> variety of ways these may be expressed (a story for another day).
>>
>> The function's return-value is passed 'across' the assignment to
>> "number_of_characters" or "seventh_times_table" (or passed directly into
>> the print() function*). The identifier will become the same data-type as
>> the result-data.
>>
>> * you will have noticed that @Alan uses the function's result within a
>> print-call rather than an assignment statement, but we are still making
>> use of the return-value.
>>
>>
>>
>> (just because this very afternoon, I've been helping someone-else who's
>> using it)
>> A free-to-download or read-on-the-web book is Al Sweigart's "Automate
>> the Boring Stuff". Chapter 3 deals with functions
>> (http://automatetheboringstuff.com/2e/chapter3/)
>> It's getting a bit old now, but the basics haven't changed...
>>
>>
>> @Alan mentioned online tutorials, quite possibly anticipating that I'd
>> chime-in with (an alternate/additional view): the suggestion of online
>> courses, eg Coursera, edX, FutureLearn, ... The advantage of these is
>> that they usually present their material in both text and video forms,
>> plus they collect a community of fellow-trainees, who will help
>> each-other with questions and readily-recognise which session/chapter
>> you're working at, right now.
>>
>> (however, re-iterating @Alan's welcome, this Discussion List is also for
>> exactly those kinds of discussions)
>>
>>
>> Disclaimer: I use the edX platform - but not for Python training.
>> --
>> Regards,
>> =dn
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