TypeError：列表索引必须是整数或切片，而不是元组列表的元组

Question

I am getting "list indices must be integers or slices, not tuple" error while trying to generate list from list of tuples. list of tuples have the following structure:

[(29208, 8, 8, 8), (29209, 8, 8, 8), (29210, 8, 8, 8), (29211, 8, 8, 8)]

The first element in the tuple is a time series, other elements are state of some variables.

The loop for converting from list of tuples to simple list is following:

TimeAxis = []

for n in lst:
    TimeAxis.append(lst[n][0])

Where lst has format as described above. For some reason it throws an error:

Traceback (most recent call last):
  File "X:\Temp\XXX_python_graph\RTT_Plot.py", line 30, in <module>
    Time.append(lst[n][0])
TypeError: list indices must be integers or slices, not tuple

I understand this is novice question, but other solutions on stackoverflow do not work. Thanks in advance.

Answer 1

Python's for loop is a Foreach construct ; you iterate over the elements of the list , not an index.

So n is one of the tuples from lst , not an index. Use it directly:

for n in lst:
    TimeAxis.append(n[0])

You could simplify your code by using a list comprehension :

TimeAxis = [tup[0] for tup in lst]

Answer 2

for n in lst:
    TimeAxis.append(n[0])

When you iterate on list, its fetching one by one element, so value of n is your every tuple, just access 0th index of it and append

Answer 3

let me help you understand, what has gone wrong in your code:

lst = [(29208, 8, 8, 8), (29209, 8, 8, 8), (29210, 8, 8, 8), (29211, 8, 8, 8)]
for n in lst:  # ns in lst -> (29208, 8, 8, 8), ... , (29211, 8, 8, 8)
    TimeAxis.append(lst[n][0]) # 1st iter: lst[(29208, 8, 8, 8)][0]

Hence the TypeError . What you probably wanted to do is:

for i in range(len(lst)):  # is in range(len(lst)) -> 0,1,2,3 
    TimeAxis.append(lst[n][0])  # 1st iter: lst[0][0]

Even though this will work, there is no need for that. There are more pythonic way, which can be found in @Martijn Pieters answer .