Importing a variable from another script and keepi

Question

I have two .py scripts. script1.py and script2.py

I am importing few variables from script2.py like:

from script2 import variable1 as var1

which works fine.

But when I update variable1 in script2.py, and then re-run script1.py, the update of variable1 doesn't show up in script1.py. Why is that so?

The update of variable1 shows up if I close IPython completely and then re-open IPython again. But I don't want to do this all the time as I need few plot's to be open.

I am using IPython 1.2.1 and Python 2.7.6 (if further info maybe needed).

Answer 1

It would be easier just to store the value in a file. For example, in the first script you would have:

myvar = 6

# do stuff

config_file = open('config.txt', 'w')
config_file.write(myvar)
config_file.close()

and in the second script you would have:

config_file_read = open('config.txt', 'r')
oldvar = int(config_file_read.read()) # you could also do float() (or any type)
config_file_read.close()

print oldvar

newvar = 5
config_file_write = open('config.txt', 'w') # this overwrites the contents of the file
config_file_write.write(str(newvar))
config_file_write.close()

Answer 2

For ipython, use the %load magic command:

In [1]: from a import x

In [2]: x
Out[2]: 20

# here go and change the content of a.py

In [3]: from a import x

In [4]: x
Out[4]: 20 # same value

In [5]: %load a.py

In [6]: # %load a.py
x = 22

In [7]: x
Out[7]: 22 # new value

Answer 3

If you have to change the variables often I think its not a good approach to write it to a python script but rather to a config file. There you could simple read it like this

def getVar(name):
    c = ConfigParser.SafeConfigParser()
    c.read('config.cfg')
    return c.get('global',name)

While the variable is written in your config.cfg file like this:

[global]
var1 = 5
var2 = 10

You could also save it as JSON and just use a json reader instead of the config reader.

In the end you can get your variable with getVar('var1') and it will always be up to date.

Answer 4

There is a way to reload modules, though it doesn't seem to work well with aliasing. You can use reload(module_name). As you'll see the docs note that your aliases wont be refreshed:

If a module imports objects from another module using from ... import ..., calling reload() for the other module does not redefine the objects imported from it — one way around this is to re-execute the from statement, another is to use import and qualified names (module.*name*) instead.

It instead suggests using

import script2 
script2.variable1

You could still alias, but you'd need to refresh the aliased names each time:

import script2
var1 = script2.variable1

...

reload(script2)
var1 = script2.variable1

If you didn't do this, var1 would hold the old value.

You could however have a quick function to do this all at once if you think it's necessary (and if it is happening often)

def reload_script2():
    global var1
    reload(script2)
    var1 = script2.variable1

Note I use global here so that var1 is modified in the global namespace, not just declared in that function. If you really only have one value you could use return var1, but I think this is a rare case where global is better.