The percentile function was added in version 1.5.x. You will need to upgrade to at least that version.

Did you try:

sudo pip install numpy==1.7.1 --upgrade

To check which version you are running, start the python console and run:

>>> import numpy
>>> print numpy.__version__

You can also do:

sudo pip freeze | grep numpy

The Ubuntu 9.10 numpy package uses version 1.3.03. It is likely that installing version 1.7.0 vai pip was successful, but your machine is defaulting to the python-numpy version instead. You can remove by running:

sudo apt-get remove python-numpy

Check the version of your pandas library:

import pandas
print(pandas.__version__)

If your version is less than 0.24.1:

pip install --upgrade pandas

In relatively recent pandas version, 1.5.2, append works, but gives a warning.

In pd 2.0, append has been removed

https://pandas.pydata.org/docs/dev/whatsnew/v2.0.0.html#deprecations

In [14]: students_classes = pd.Series({'Alice': 'Physics',
    ...:                    'Jack': 'Chemistry',
    ...:                    'Molly': 'English',
    ...:                    'Sam': 'History'})
    ...: kelly_classes = pd.Series(['Philosophy', 'Arts', 'Math'], index=['Kelly', 'Kelly', 'Kelly'])

In [15]: students_classes.append(kelly_classes)
C:\Users\paul\AppData\Local\Temp\ipykernel_6072\990183765.py:1: FutureWarning: The series.append method is deprecated and will be removed from pandas in a future version. Use pandas.concat instead.
  students_classes.append(kelly_classes)
Out[15]: 
Alice       Physics
Jack      Chemistry
Molly       English
Sam         History
Kelly    Philosophy
Kelly          Arts
Kelly          Math
dtype: object

Under the covers, append method uses _append, which works without raising the warning:

In [16]: students_classes._append(kelly_classes)
Out[16]: 
Alice       Physics
Jack      Chemistry
Molly       English
Sam         History
Kelly    Philosophy
Kelly          Arts
Kelly          Math
dtype: object

And using the recommended concat:

In [18]: pd.concat([students_classes,kelly_classes])
Out[18]: 
Alice       Physics
Jack      Chemistry
Molly       English
Sam         History
Kelly    Philosophy
Kelly          Arts
Kelly          Math
dtype: object

Python lists have an efficient append method. numpy has a np.append function which is a poorly named cover for calling np.concatenate, and is often misused (it shouldn't be used iteratively). pandas may be trying to avoid similar problems by getting rid of the append method. With pd.concat you can join many Series (or frames) at once, and aren't (as) tempted to use it in a loop.

Looking up the code for _append (which is still in 2.0), I see it ends up using pd.concat. So there's no value in using this 'work-around'. Use concat as recommended.