Styjun

I'm working on some kind of software that will generate bass guitar tabs (only using 4 strings and frets 0-12
i tried defining these globals everywhere but it does't work.
Also what is the error about caling the function?

Errors:

Traceback (most recent call last):
File "/home/olaf/Documents/Projects/BassComposer/main.py", line 69, in
generator(fret, string)
File "/home/olaf/Documents/Projects/BassComposer/main.py", line 62, in generator
tab3 += str(fret)
NameError: name 'tab3' is not defined

from random import randint

try:
 times =str(int(input("How many notes do you want to be created?nn")))
except:
 print("nInvalid input!n")

print("nnGenerating " + times + " note(s) long basslinen...nn")

startString = randint(0, 3)
startFret = randint(0, 9)

string = startString
fret = startFret

notes = int(times)




def generator(fret, string):
 global tab0
 global tab1
 global tab2
 global tab3
 x = randint(0,11)
 y = randint(0,16)
 if x in range(4, 9):
 if x in range(4, 7) and fret in range(0,11):
 fret += 1
 if x in range(4, 5) and fret in range(0, 11):
 fret += 1
 if x in range(8,11) and fret in range(1,12):
 fret -= 1
 if x in range(10,11) and fret in range(1, 12):
 fret -= 1
 if y in range(11,16):
 if y in range(11, 13) and string in range(0,2):
 string += 1
 if (y == 13) and string in range(0,2):
 string += 1
 if y in range(14, 16) and string in range(1, 3):
 fret -= 1
 if (y==16) and string in range(1, 3):
 fret -= 1
 if string == 0:
 tab0 += str(fret)
 tab1 += " "
 tab2 += " "
 tab3 += " "
 if string == 1:
 tab1 += str(fret)
 tab0 += " "
 tab2 += " "
 tab3 += " "
 if string == 2:
 tab2 += str(fret)
 tab0 += " "
 tab1 += " "
 tab3 += " "
 if string == 3:
 tab3 += str(fret)
 tab0 += " "
 tab1 += " "
 tab2 += " "


for notes in range(0, notes):
 generator(fret, string)
 notes -= 1

I would be thankfull if someone told me what are these problems caused by and how to fix them

global is the statement that declares the scope of the variable, not creates it. If you want your code to just work, you should write this before the generator function:

tab0 = ""
tab1 = ""
tab2 = ""
tab3 = ""

...BUT!

This is very bad practice. In addition, your code has several another serious problems, that don't cause errors, but makes your code very unclear and hard to maintain. So let's fix them and make your code beautiful :)

1. Global variables and global statement are very bad practice. You can never be sure that some global variable will be correct and have the value you expect to see. In 99.9% cases global variable usage is not an option and can be replaced by local variables. If you really need global statement, you can use some kind of configuration files. Your generator function changes the state of four global variables and doesn't store the result, and we can rewrite it with:

def generator(fret, string):
 tab0 = ""
 tab1 = ""
 tab2 = ""
 tab3 = ""
 for notes in range(0, notes):
 # All your another code
 return tab0, tab1, tab2, tab3
...
tab0, tab1, tab2, tab3 = generator(...)

2. You have four logically equal variables: tab0, tab1, tab2, tab3. What if somebody will want to run this code for 6-tabs bass guitar? In reality our tabs are the part of the one entity - tab... err... table (I'm not a musician, sorry). So we can combine them into one entity - tab list!

tab_list = []

With it, our code:

tab0 += str(fret)
tab1 += " "
tab2 += " "
tab3 += " "

converts to:

tab_list.append((str(fret), None, None, None)) (don't worry about Nones, we can tranform them later)

Now we have this code:

 if string == 0:
 tab_list.append(str(fret), None, None, None)
 if string == 1:
 tab_list.append(None, str(fret), None, None)
 if string == 2:
 tab_list.append(None, None, str(fret), None)
 if string == 3:
 tab_list.append(None, None, None, str(fret))

See the pattern? :) The str(fret) index is equal to string value! So we compress it even more:

 tabs_to_append = [None, None, None, None]
 tabs_to_append[string] = str(fret)
 tab_list.append(tabs_to_append)

And we compress 20 lines of code into 3!

3. This part of code:

for notes in range(0, notes):
 generator(fret, string)
 notes -= 1

iterates for 0..notes, but! the index name is equal to range bound and changes inside. It is very, very, VERY bad practice! It this case it will work (and it is strange), but in the most cases it will have many unexpected results that will force you to debug them hour by hour. So we rewrite it as:

for _ in range(0, notes): # We don't really need this index

4. Unnesessary logics:

I will explain this part on this piece of code:

1. if x in range(4, 9):
2. if x in range(4, 7) and fret in range(0,11):
3. fret += 1
4. if x in range(4, 5) and fret in range(0, 11):
5. fret += 1

You have the first if-statement that checks x is 4..9. But inside there is only one if-statement that checks x is 4..7. It means the first if-statement is useless so we can just remove it (or there is a logical error inside). In addition, both if-statement on lines 2 and 4 has fret in range(0, 11). We can move it to the first line and get this code:

1. if fret in range(0,11):
2. if x in range(4, 7):
3. fret += 1
4. if x in range(4, 5):
5. fret += 1

Now look at if-statement on line 4. range(4, 5) returns one item list [4]. So this line transforms to: if x == 4:. Now we can finally change our block of code:

1. if fret in range(0,11):
2. if x in range(5, 7):
3. fret += 1
4. elif x == 4:
5. fret += 2

You can transform your other blocks of logic code. I am sure it will be simplified a lot (maybe even be merged with the block we rewrited now).

And finally we have our new program:

from random import randint

try:
 times = int(input("How many notes do you want to be created?nn"))
except:
 print("nInvalid input!n")

print("nnGenerating " + str(times) + " note(s) long basslinen...nn")

startString = randint(0, 3)
startFret = randint(0, 9)


def generator(startFret, startString, times):
 string = startString
 fret = startFret
 tab_list = []

 for _ in range(times):
 x = randint(0, 11)
 y = randint(0, 16)

 # Transformed
 if fret in range(0,11):
 if x in range(5, 7):
 fret += 1
 elif x == 4:
 fret += 2

 # Old, removed unnesessary if-statements
 if x in range(8,11) and fret in range(1,12):
 fret -= 1
 if x in range(10,11):
 fret -= 1
 if y in range(11, 13) and string in range(0,2):
 string += 1
 if (y == 13):
 string += 1
 if y in range(14, 16) and string in range(1, 3):
 fret -= 1
 if (y==16):
 fret -= 1

 tabs_to_append = ["_", "_", "_", "_"]
 tabs_to_append[string] = str(fret)
 tab_list.append(tabs_to_append)
 return tab_list

tabs = generator(startFret, startString, times)

# Converts list of time-tabs to strings of tabs-timeline
tabs_str = [
 " ".join([
 tabs[i][j]
 for i in range(len(tabs))
 ])
 for j in range(4)
]
for s in tabs_str:
 print(s)

It can be enhanced more (of course, nearly every program can :) ), but I am extremely tired, sorry. I think I helped you a bit with my long-long digital papyrus.

P.S. Your generator returns tabs for only one tab. I think you have a logical error inside your generator code. I don't know what are you want to generate so I will not give you any advices.