XueLab

• Pass parameters in command line

# test.py name_1 name_2 ... name_n
# or python -i test.py name_1 name_2 ... name_n
import sys
parms = sys.argv  # return ['test.py", name_1, ... name_n]

• Execute an external command

import os
os.system('ls')

• time counter (tic/toc)

import time
tic = time.time()
... ...
toc = time.time()
elaps = toc-tic

• http://stackoverflow.com/questions/860140/whoami-in-python

• Find the newest/oldest file in a path: http://code.activestate.com/recipes/576804-find-the-oldest-or-yougest-of-a-list-of-files/

• Answer: use zip() in combination with a special unitary operator “*” which release elements from a list/tuple (i.e., effectively it removes “()” or “[]”). ( Ref1, Ref2) For example:

a = [1, 2, 3]
b = ['A', 'B', 'C']
z = zip(a, b)
# to reverse it
a, b = zip(*z)

• Ref
• In Python 2.6 (or earlier), use the dict constructor:

d = dict((key, value) for (key, value) in sequence)

• In Python 2.7+ or 3, you can just use the dict comprehension syntax directly:

d = {key: value for (key, value) in sequence}

• Output plots into a multi-page pdf file

from matplotlib.backends.backend_pdf import PdfPages
 
fnpdf = 'out.pdf'
pdf = PdfPages(fnpdf)
 
...
 
for i in range(npage):
    ...
    pdf.savefig()
    show()  # you can remove this line if needed
 
pdf.close()