when running import nltk, Syntax Error is displayed
You shouldn't be developing using python 2.7 anymore, 3.xx has been out for a long time and 2.x was EOL'd recently. Mac OS X has python3 installed as /usr/bin/python3.
To fix this error, you'll need to add from future import print_function at the top of /Users/zineb/.local/lib/python2.7/site-packages/nltk/probability.py.
File "/Users/zineb/.local/lib/python2.7/site-packages/nltk/probability.py", line 333
print("%*s" % (width, samples[i]), end=" ")
                                          ^
SyntaxError: invalid syntax