improving speed of Python module import

The question of how to speed up importing of Python modules has been asked previously (https://stackoverflow.com/questions/2010255/speeding-up-the-python-import-loader and https://stackoverflow.com/questions/6025635/python-speed-up-imports) but without specific examples and has not yielded accepted solutions. I will therefore take up the issue again here, but this time with a specific example.

I have a Python script that loads a 3-D image stack from disk, smooths it, and displays it as a movie. I call this script from the system command prompt when I want to quickly view my data. I'm OK with the 700 ms it takes to smooth the data as this is comparable to MATLAB. However, it takes an additional 650 ms to import the modules. So from the user's perspective the Python code runs at half the speed.

This is the series of modules I'm importing:

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as animation
import scipy.ndimage
import scipy.signal
import sys
import os

Of course, not all modules are equally slow to import. The chief culprits are:

matplotlib.pyplot   [300ms]
numpy               [110ms]
scipy.signal        [200ms]

I have experimented with using from, but this isn't any faster. Since Matplotlib is the main culprit and it's got a reputation for slow screen updates, I looked for alternatives. One is PyQtGraph, but that takes 550 ms to import.

I am aware of one obvious solution, which is to call my function from an interactive Python session rather than the system command prompt. This is fine but it's too MATLAB-like, I'd prefer the elegance of having my function available from the system prompt.

I'm new to Python and I'm not sure how to proceed at this point. Since I'm new, I'd appreciate links on how to implement proposed solutions. Ideally, I'm looking for a simple solution (aren't we all!) because the code needs to be portable between multiple Mac and Linux machines.

Not an actual answer to the question, but a hint on how to profile the import speed with Python 3.7 and tuna (a small project of mine):

python3 -X importtime -c "import scipy" 2> scipy.log
tuna scipy.log

you could build a simple server/client, the server running continuously making and updating the plot, and the client just communicating the next file to process.

I wrote a simple server/client example based on the basic example from the socket module docs: http://docs.python.org/2/library/socket.html#example

here is server.py:

# expensive imports
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as animation
import scipy.ndimage
import scipy.signal
import sys
import os

# Echo server program
import socket

HOST = ''                 # Symbolic name meaning all available interfaces
PORT = 50007              # Arbitrary non-privileged port
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((HOST, PORT))
s.listen(1)
while 1:
    conn, addr = s.accept()
    print 'Connected by', addr
    data = conn.recv(1024)
    if not data: break
    conn.sendall("PLOTTING:" + data)
    # update plot
    conn.close()

and client.py:

# Echo client program
import socket
import sys

HOST = ''    # The remote host
PORT = 50007              # The same port as used by the server
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((HOST, PORT))
s.sendall(sys.argv[1])
data = s.recv(1024)
s.close()
print 'Received', repr(data)

you just run the server:

python server.py

which does the imports, then the client just sends via the socket the filename of the new file to plot:

python client.py mytextfile.txt

then the server updates the plot.

On my machine running your imports take 0.6 seconds, while running client.py 0.03 seconds.

You can import your modules manually instead, using imp. See documentation here.

For example, import numpy as np could probably be written as

import imp
np = imp.load_module("numpy",None,"/usr/lib/python2.7/dist-packages/numpy",('','',5))

This will spare python from browsing your entire sys.path to find the desired packages.

See also:

https://stackoverflow.com/questions/35964825/manually-importing-gtk-fails-module-not-found/36119115#36119115

1.35 seconds isn't long, but I suppose if you're used to half that for a "quick check" then perhaps it seems so.

Andrea suggests a simple client/server setup, but it seems to me that you could just as easily call a very slight modification of your script and keep it's console window open while you work:

• Call the script, which does the imports then waits for input
• Minimize the console window, switch to your work, whatever: *Do work*
• Select the console again
• Provide the script with some sort of input
• Receive the results with no import overhead
• Switch away from the script again while it happily awaits input

I assume your script is identical every time, ie you don't need to give it image stack location or any particular commands each time (but these are easy to do as well!).

Example RAAC's_Script.py:

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as animation
import scipy.ndimage
import scipy.signal
import sys
import os

print('********* RAAC\'s Script Now Running *********')

while True: # Loops forever
	# Display a message and wait for user to enter text followed by enter key.
	# In this case, we're not expecting any text at all and if there is any it's ignored
	input('Press Enter to test image stack...')
	
	'''
	*
	*
	**RAAC's Code Goes Here** (Make sure it's indented/inside the while loop!)
	*
	*
	'''

To end the script, close the console window or press ctrl+c.

I've made this as simple as possible, but it would require very little extra to handle things like quitting nicely, doing slightly different things based on input, etc.

You can use lazy imports, but it depends on your use case.

If it's an application, you can run necessary modules for GUI, then after window is loaded, you can import all your modules.

If it's a module and user do not use all the dependencies, you can import inside function.

[warning] It's against pep8 i think and it's not recomennded at some places, but all the reason behind this is mostly readability (i may be wrong though...) and some builders (e.g. pyinstaller) bundling (which can be solved with adding missing dependencies param to spec)

If you use lazy imports, use comments so user knows that there are extra dependencies.

Example:

import numpy as np

# Lazy imports
# import matplotlib.pyplot as plt

def plot():
    import matplotlib.pyplot as plt
    
    # Your function here
    # This will be imported during runtime 

For some specific libraries i think it's necessity.

You can also create some let's call it api in __init__.py

For example on scikit learn. If you import sklearn and then call some model, it's not found and raise error. You need to be more specific then and import directly submodule. Though it can be unconvenient for users, it's imho good practice and can reduce import times significantly.

Usually 10% of imported libraries cost 90% of import time. Very simple tool for analysis is line_profiler

import line_profiler
import atexit

profile = line_profiler.LineProfiler()
atexit.register(profile.print_stats)

@profile
def profiled_function():

    import numpy as np
    import pandas as pd
    import matplotlib.pyplot as plt


profiled_function()

This give results

Line #      Hits         Time  Per Hit   % Time  Line Contents
==============================================================
    20                                               @profile
    21                                               def profiled_function():
    22
    23         1    2351852.0 2351852.0      6.5          import numpy as np
    24         1    6545679.0 6545679.0     18.0          import pandas as pd
    25         1   27485437.0 27485437.0     75.5          import matplotlib.pyplot as plt

75% of three libraries imports time is matplotlib (this does not mean that it's bad written, it just needs a lot of stuff for grafic output)

Note:

If you import library in one module, other imports cost nothing, it's globally shared...

Another note:

If using imports directly from python (e.g pathlib, subprocess etc.) do not use lazy load, python modules import times are close to zero and don't need to be optimized from my experience...