from the desk of stinkpot

to insert a timestamp into your python code: import time …. print time.localtime()

profiling running time in python is straightforward.  what’s tricky is measuring how much memory your program is consuming.  i’ve modified some code i found online to do the trick nicely; just import this PyVM module and insert the following into your program: import PyVM … PyVM.MemoryUpdate(“memory usage here”) PyVM.MemoryUpdate(“memory usage there”) PyVM.MemoryUpdate(“memory usage etc.”) what […]

let’s say you’ve got two lists creatively named: list1 & list2, and you’d like their intersection. an easy way to get this intersection would be to iterate through both lists: intersect = filter(lambda i: i in list1,list2) this is slow though for large lists, as it takes roughly M X N steps, where M and […]

here’s how to extract every other element from a python list using one line of code. to get even elements, use “i%2 == 0″; for odd elements, use “i%2 == 1″. >>> my_list = ['banana','apple','frog','octopus','pen','spiderman','flower','battery'] >>> map(lambda i: my_list[i],filter(lambda i: i%2 == 0,range(len(my_list)))) ['banana', 'frog', 'pen', 'flower'] >>> map(lambda i: my_list[i],filter(lambda i: i%2 == 1,range(len(my_list)))) […]

to flush a write buffer in python on filehandle f: f.flush() nice and easy …

to write out a matrix from python’s numpy: import numpy numpy.savetxt(matrix_filename,matrix_object) to read a matrix from numpy: import numpy matrix_object = numpy.genfromtxt(matrix_filename)

to write a python dict to a text file: f = open(‘text.file’,’w’) f.write(my_dict) to read a python dict from a text file: f = open(‘text.file’,’r’) my_dict = eval(f.read())

to hash a set in python, you need to make it immutable: from sets import Set … this_set = frozenset(i) my_dict[this_set] = 1

as long as you’re running a version of python newer than 2.3, you can easily call the python profiler to find bottlenecks in your code: $ python -m cProfile mycode.py

if your python code produces the following error: “RuntimeError: maximum recursion depth exceeded in cmp,” try adding this line to the beginning of your code: sys.setrecursionlimit(1500) note that python’s default limit is 1000.