Posts: 83
Threads: 33
Joined: Dec 2017
I feel I'm shaky on understanding the interplay between passing variables through functions (outside of classes)...Basically IDK when to use foo() vs foo(bar) especially in freestanding (OUTSIDE of a class) nested functions. 
PLEASE HELP
I wrote this up. it's a self contained script:
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import sys
from functools import partial as p
def inquire(a,type,errmsg):
while True:
b = input(a)
if b !='':
try:
b == type(b)
except ValueError:
print('{}'.format(errmsg))
continue
else:
print('ok')
return b
else:
print(f'{a:^50} must be answered.')
continue
the_q = p(inquire,type=str,errmsg='sorry')
def foo():
while True:
quit_now = the_q('\'y\' to quit anything else to continue')
quit_now.strip().lower()
if quit_now =='y' or quit_now =='yes':
sys.exit()
else:
bar()
continue
def bar():
quest=the_q('please enter a, b, c, d or etc.')
quest.strip().lower()
if quest == 'a':
forA(quest)
elif quest == 'b':
forB()
elif quest == 'c':
forC(quest)
elif quest == 'd':
forD()
elif quest == 'e':
forE(quest)
else:
forEtc()
def forA(x):
print(f'{x:^10}is fine.')
def forB():
global someVariable
print('nothing...'.format(someVariable))
def forC(y):
print('{} works too...'.format(y))
def forD():
print('fine')
def forE(someVariable):
global quest
print('should work...'.format(someVariable))
def forEtc():
print('works')
if __name__=='__main__':
foo()
else:
print('sorry {__name__} not main')
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It works. Except for [input]b[/input]
this triggers
Error: Traceback (most recent call last):
File "defexp0.py", line 77, in <module>
foo()
File "defexp0.py", line 30, in foo
bar()
File "defexp0.py", line 39, in bar
forB()#won't work
File "defexp0.py", line 54, in forB
print('nothing...'.format(someVariable))
NameError: name 'someVariable' is not defined
Perhaps someone could clarify foo() vs foo(bar) and their nuances in nested functions? Please?
Posts: 3,458
Threads: 101
Joined: Sep 2016
Think of a function as a sort of black box. You give it some data to work with, it does *something*, and then gives you a return value. A function shouldn't use any value that isn't passed to it. global should be avoided at all costs.
Posts: 83
Threads: 33
Joined: Dec 2017
(Feb-24-2018, 06:13 PM)nilamo Wrote: Think of a function as a sort of black box. You give it some data to work with, it does *something*, and then gives you a return value. Yes. And it works wonderfully well when functions are part of a class.
Quote:A function shouldn't use any value that isn't passed to it.
this is where I get frustrated lol. Pls see code in op above. Entire script runs off foo(). Not a single parameter, but quite a few variable gets assigned values in its body....
So this is what keeps getting me and textbooks seems to not care about the discrepency
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def foo():
a = 'moo'
print(a)
bar()
def bar():
print('bar function')
if __name__=='__main__':
foo()
else:
print('choosing not to run')
|
this script runs...this bothers me.
Maybe it's a detail that comes from experience but I never feel certain when I can make do with foo() and when I need foo(param)....
Posts: 7,312
Threads: 123
Joined: Sep 2016
Feb-25-2018, 01:10 AM
(This post was last modified: Feb-25-2018, 01:10 AM by snippsat.)
(Feb-24-2018, 09:14 PM)mepyyeti Wrote: this script runs...this bothers me.
Maybe it's a detail that comes from experience but I never feel certain when I can make do with foo() and when I need foo(param).... Make it clear that foo takes a augment.
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def foo(bar):
a = 'moo'
print(a)
bar()
def bar():
print('bar function')
if __name__=='__main__':
foo(bar)
else:
print('choosing not to run')
|
Quote:this is where I get frustrated lol. Pls see code in op above. Entire script runs off foo().
That's normal to have a function that run whole script,the design bit can be the hard part to figure out.
Clearer name(like eg menu) and never ever global,make it clear that a function take arguments,not to long functions.
Can be some tips.
Example no variables in global name namespace,calling menu start it.
result function takes 2 argumet, coin_flip and user_choice these function do only one task each.
Always fall back to menu where can play again or Quit out.
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import random
def coin_flip():
return random.choice(('head', 'tail'))
def user_choice():
command = input("Choose Head or Tail: ").lower()
return command
def result(coin_flip, user_choice):
coin = coin_flip()
choice = user_choice()
if coin == choice:
print(f'\nComputer <{coin}> You gussed <{choice}> which is correct\n')
else:
print(f'\nComputer <{coin}> You gussed <{choice}> which is wrong\n')
def menu():
while True:
print('(1) Coin flip game')
print('(Q) Quit\n')
choice = input('Enter your choice: ').lower()
if choice == '1':
result(coin_flip, user_choice)
elif choice == 'q':
return False
else:
print(f'Not a correct choice: {choice}')
if __name__ == '__main__':
menu()
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If function get to complicated to design use a class 
Posts: 83
Threads: 33
Joined: Dec 2017
Feb-25-2018, 03:48 AM
(This post was last modified: Feb-25-2018, 03:49 AM by mepyyeti.)
SO with the 1st snippet:
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def foo(bar):
a = 'moo'
print(a)
bar()
def bar():
print('bar function')
if __name__=='__main__':
foo(bar)
else:
print('choosing not to run')
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since both foo() and foo(bar) work to execute the script...is it simply a matter of best practices to just use foo(bar) to run the script? Technically, whether or not I have a parameter doesn't seem too matter...
Regarding the snippet you wrote:
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import random
def coin_flip():
return random.choice(('head', 'tail'))
def user_choice():
command = input("Choose Head or Tail: ").lower()
return command
def result(coin_flip, user_choice):
coin = coin_flip()
choice = user_choice()
if coin == choice:
print(f'\nComputer <{coin}> You gussed <{choice}> which is correct\n')
else:
print(f'\nComputer <{coin}> You gussed <{choice}> which is wrong\n')
def menu():
while True:
print('(1) Coin flip game')
print('(Q) Quit\n')
choice = input('Enter your choice: ').lower()
if choice == '1':
result(coin_flip, user_choice)
elif choice == 'q':
return False
else:
print(f'Not a correct choice: {choice}')
if __name__ == '__main__':
menu()
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user_choice() clearly creates a variable, command, and gives it a value but necessitates no parameter. Yet, result(*args) also creates variables,coin and choice, and gives them the returned value of the 2 executed functions, coin_flip and user_choice.
why not just say:
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...
def result():
coin = coin_flip()
choice = user_choice()
...
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the logic works fine for
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...
def user_choice():
command = input("Choose Head or Tail: ").lower()
return command
...
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Question boils down to : Why do I need to set up parameters at all. user_choice() shows that I can create variables without parameters (technically just 1 positional)? this is where I get tripped up...
Posts: 7,312
Threads: 123
Joined: Sep 2016
(Feb-25-2018, 03:48 AM)mepyyeti Wrote: Why do I need to set up parameters at all. user_choice() shows that I can create variables without parameters To make it clear and more readable that a function take in code in from outside.
The black box model as @ nilamo talk abot crash as son as a function,variable,list,ect... magically appear in a function when is not set as parameter.
As soon as this happen you wonder where dos it come from has it a relationship with this function?
It can be easy to see in shorter code as my example,in larger code it can be a pain that stuff just magically appear from somewhere else.
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