我怎么能 append 一个字符串到列表中的元组？

Question

I'm creating an application that generates walking bass lines from specified chords. It always begins with the root (1st chord tone), then the permutations of the 1st, 3rd and 5th chord tones follow.

I'd like to append a string (the root) to the tuples (the permutations) in a list in Python, but my code doesn't work. Let me put my code:

# pip install pychord

from pychord import Chord
from itertools import permutations 

def returnPermutations(arr, r): 
    return list(permutations(arr, r))

c7 = Chord("C7")
print("c7.components()", c7.components())
print("Get the Triad: c7.components()[0:3]: ", c7.components()[0:3])

chordTonePermutations = returnPermutations(c7.components()[0:3], 3)
print("chordTonePermutations: ", chordTonePermutations)
print("chordTonePermutations[0]: ", chordTonePermutations[0])

# walkingBass = tuple((c7.components()[0],)) + chordTonePermutations[0]
walkingBass = list(tuple((c7.components()[0],)) + chordTonePermutations[0])

walkingBassList = []
# walkingBassList = list.append(walkingBass)

for chordTones in chordTonePermutations:
  print("chordTones", chordTones)
  walkingBass = tuple((c7.components()[0],)) + chordTones
  # walkingBass = list(tuple((c7.components()[0],)) + chordTones)
  walkingBassList = list.append(walkingBass)

print("walkingBass", walkingBass)

print("walkingBassList", walkingBassList)
# What I expect is a list of tuples which always begins with the root 'C', 
# plus the permutations of the triad (the first 3 chord tones):
# walkingBassList [
# ('C', 'C', 'E', 'G'), 
# ('C', 'C', 'G', 'E'), 
# ('C', 'E', 'C', 'G'), 
# ('C', 'E', 'G', 'C'), 
# ('C', 'G', 'C', 'E'), 
# ('C', 'G', 'E', 'C')]

... This code gives me the following output with an error:

c7.components() ['C', 'E', 'G', 'Bb']
Get the Triad: c7.components()[0:3]:  ['C', 'E', 'G']
chordTonePermutations:  [('C', 'E', 'G'), ('C', 'G', 'E'), ('E', 'C', 'G'), ('E', 'G', 'C'), ('G', 'C', 'E'), ('G', 'E', 'C')]
chordTonePermutations[0]:  ('C', 'E', 'G')
chordTones ('C', 'E', 'G')
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-84-3a01c9d6da74> in <module>()
     24   walkingBass = tuple((c7.components()[0],)) + chordTones
     25   # walkingBass = list(tuple((c7.components()[0],)) + chordTones)
---> 26   walkingBassList = list.append(walkingBass)
     27 
     28 print("walkingBass", walkingBass)

TypeError: descriptor 'append' requires a 'list' object but received a 'tuple'

So, I surrounded the tuple with a list:

  # walkingBass = tuple((c7.components()[0],)) + chordTones
  walkingBass = list(tuple((c7.components()[0],)) + chordTones)

Now it gives me TypeError: append() takes exactly one argument (0 given) :

TypeError                                 Traceback (most recent call last)
<ipython-input-86-e2ecc32a34c8> in <module>()
     24   # walkingBass = tuple((c7.components()[0],)) + chordTones
     25   walkingBass = list(tuple((c7.components()[0],)) + chordTones)
---> 26   walkingBassList = list.append(walkingBass)
     27 
     28 print("walkingBass", walkingBass)

TypeError: append() takes exactly one argument (0 given)

... Wait. (0 given)? One argument walkingBass is already given, right? What's wrong with me?

The following question doesn't help me because the append really doesn't have any argument. It keeps saying: TypeError: append() takes exactly one argument (0 given)

... I'm totally confused. Could anyone help me to fix this? Thank you in advance.

Answer 1

You're trying to invoke append as a function, but it's a method. So instead of doing:

walkingBassList = list.append(walkingBass)

You need to do:

walkingBassList.append(walkingBass)

In the append method, self gets bound to walkingBassList so it knows what to append to. Without that information, there isn't much it could do.

Answer 2

walkingBassList = list.append(walkingBass)

should be

walkingBassList.append(walkingBass)