I have two files and for some reason I do not want to define my variable as an input in my function:
function.py
def test():
print(var)
if __name__ == '__main__':
var = "test"
test()
call_function.py
from function import *
global var
var = "test"
test()
If I do this i get an error saying that var is not defined. How can I solve this ?
You can do something like this, but the fact that this works does not mean that it is a good thing to do, DO NOT CODE LIKE THIS.
from function import *
var = ['I WILL FIRE YOU IF I SEE CODE LIKE THIS IN AN APPLICATION']
test.__globals__['var'] = var
test() # output: ['I WILL FIRE YOU IF I SEE CODE LIKE THIS IN AN APPLICATION']
var[0] = "DO NOT DO THIS, YOU'LL BREAK SOMETHING IF YOU DON'T KNOW WHAT ARE YOU DOING"
test() # output: ["DO NOT DO THIS, YOU'LL BREAK SOMETHING IF YOU DON'T KNOW WHAT ARE YOU DOING"]
Related
In this code I want to compare the previous message with the current message. So I created a variable to save the previous message. I wanted to create it as a static variable then manipulate it inside the code. but the outside the x function if I declare the variable it shows an error.
flag = 1
previousMessage = "abc"
def x():
do_something
currentMessage = m #got a string from code
if(currentMessage==previousMessage):
#shows error in flag and previousMessgae
#says create parameter of previousMessage and flag
flag=0
return
else:
do_something
previousNews=currentNews
flag=1
return
def call():
while True:
if(flag==1)
x()
time.sleep(60)
elsif(flag==0)
time.sleep(60) **strong text**
call()
Not sure if this is what you need. Try adding global before flag and previousMessage to make that variable a global variable.
Say for example I got the code:
def getRoute(getRouteFile):
getRoutePath = []
routeFile = open(getRouteFile, "r")
for routes in routeFile:
getRoutePath.append(map(ord, routes.split('>')))
return getRoutePath
If I do a function such as which would try and call the items in the getRoutePath array from a function called:
def routeCalculation(getRoute,nodeTable, currentNode):
How do I call it? I tried doing these:
def routeCalculation(getRoute,nodeTable, currentNode):
route = getRoutePath
def routeCalculation(getRoute,nodeTable, currentNode):
route = getRoute[getRouthPath]
And none seem to work. Can anyone help me?
Whenever you declare a variable in a function, when you exit the function, the variable is destroyed. Example:
a = ""
def function():
a = "hello"
b = "hello"
print(a) #prints "hello" because a was declared outside of the function
print(b) #does not print anything
This is called "scope", and if you have a problem understanding it, you should search up a tutorial about it. In order to fix your problem move the code getRoutePath = [] outside of your functions.
I want to get inner function result so i code it like
def main():
def sub():
a = 1
print a
exec main.__code__.co_consts[1]
using above code working successfully but i want to pass the argument to the sub function like...
def main():
def sub(x):
a = x + 1
return a
ans = exec main.__code__.co_consts[1]
print ans
in that problem is i don't know how to pass that x value.
that work must need to exec so that how to pass that x value with exec without interaction of main function
Maybe something like the code below, as suggested by this SO answer
def main():
def sub():
a = x + 1
print a
return a
exec(main.__code__.co_consts[1], {'x': 1} )
How can I use external variables in Python, like extern int x; in C?
For example,
main1.py:
from myfunc import print_a
a = 10
print a
print_a()
myfunc.py:
def print_a():
global a
print a
Simply re-assign the variable in the module:
import myfunc
from myfunc import print_a
a = 10
print a
myfunc.a = a
print_a()
Otherwise it is not possible.
Rememeber that python treats modules in a way that is quite different from C.
The import in python does not "copy the contents" of the file in that place,
but it executes the code in the given file and creates a module object.
The global variable of the module are the module object attributes, which can be modified as I've shown. There is no such notion as "global variable" except for built-ins.
I'd suggest to refactor your code in such a way that you don't have to modify this global variable at all, moving the code that uses myfunc.a from main1 to myfunc.
The fact that you need such global variable is already a code smell that there's something wrong with your code and you should try to fix it.
Actually there is a way to affect the "global scope" but it is so hackish that I don't even want to mention it. Trust me: you don't want to use it. If people see your code using such a hack you may be in physical danger.
Unlike C, variables declared at global scope are still limited in scope to the module they are created in, so you need to qualify the name a with the module it lives in.
The global keyword is used when you are going to modify a global variable by reassigning, you do not need it when you are just referencing a global variable.
If you are trying to access a variable of another file, you must import that module, and because of the way your files are structured you have a couple of ways to resolve issues:
Option 1) Move the referencing of myfunc.print_a inside of a function and import main1 inside myfunc to see a
main1.py
import myfunc
a = 10
def main():
print a
myfunc.print_a()
if __name__ == '__main__':
main()
myfunc.py
import main1
def print_a():
print main1.a
Option 2) recommended Move the variable(s) into another module and have both myfunc and main1 import it.
vals.py
a = 20
main1.py
import vals
from myfunc import print_a
vals.a = 10
print vals.a
print_a()
myfunc.py
import vals
def print_a():
print vals.a
This is a workaround to this problem by using a common external file. In this example I am storing an index variable to flag in each application whether a file is being accessed. The variable indxOpen in ext1.py and indxO in ext2.py are being updated and stored in a common external text file "externalVars.txt"
lead application ext1.py
# lead application ext1.py
#this alternately flips the value of indxOpen on prime number intervals
import time
def update(d,v1):
f=open(d+'externalVars.txt','r+')
f.write(str( v1))
f.truncate()
f.close()
# ensure variable is initialised and made available to external apps
indxOpen = False
var_dir = "<your external var directory>/"
try:
f =open(var_dir+'externalVars.txt','r')
except:
f= open(var_dir+'externalVars.txt','w')
f.close()
# this alternately flips the value of indxOpen on prime number intervals
update(var_dir,indxOpen)
i = 0
while True:
while indxOpen:
i += 1
if (i % 13) ==0:
indxOpen = indxOpen ^ True
update(var_dir,indxOpen)
f=open(var_dir+'externalVars.txt','r+')
t=f.readline()
print "app1",t," ",i
if t=='False':
print "app1 updated"
update(var_dir,indxOpen)
indxOpen = False
else:
time.sleep(1.4)
while not indxOpen:
f=open(var_dir+"externalVars.txt","r+")
t=f.readline()
print "app1",t
if t=='True':
indxOpen = True
else:
time.sleep(1)
ext2.py following application
# ext2.py this alternately flips the value of indxO on prime number intervals but it is initialised by the lead application
# in this case ext1.py
# python 2.7.12
import time
def update(d,v1):
f=open(d+'externalVars.txt','r+')
f.write(str( v1))
f.truncate()
f.close()
var_dir = "<your external var directory>/"
# intialise external variable
f=open(var_dir+'externalVars.txt','r+')
t=f.readline()
if t=='True':
indxO= True
if t=='False':
indxO= False
i=0
while True:
while indxO:
f=open(var_dir+"externalVars.txt","r+")
t=f.readline()
print "app2",t
if t=='False':
indxO = False
update(var_dir,indxO)
else:
time.sleep(1.5)
while not indxO:
i += 1
if (i % 17) ==0:
indxO = indxO ^ True
update(var_dir,indxO)
f=open(var_dir+"externalVars.txt","r+")
t=f.readline()
print "app2",t," ",i
if t=='True':
indxO = True
print "apt2 updated"
update(var_dir,indxO)
else:
time.sleep(1.3)
Let's say we have a module m:
var = None
def get_var():
return var
def set_var(v):
var = v
This will not work as expected, because set_var() will not store v in the module-wide var. It will create a local variable var instead.
So I need a way of referring the module m from within set_var(), which itself is a member of module m. How should I do this?
def set_var(v):
global var
var = v
The global keyword will allow you to change global variables from within in a function.
As Jeffrey Aylesworth's answer shows, you don't actually need a reference to the local module to achieve the OP's aim. The global keyword can achieve this aim.
However for the sake of answering the OP title, How to refer to the local module in Python?:
import sys
var = None
def set_var(v):
sys.modules[__name__].var = v
def get_var():
return var
As a follow up to Jeffrey's answer, I would like to add that, in Python 3, you can more generally access a variable from the closest enclosing scope:
def set_local_var():
var = None
def set_var(v):
nonlocal var
var = v
return (var, set_var)
# Test:
(my_var, my_set) = set_local_var()
print my_var # None
my_set(3)
print my_var # Should now be 3
(Caveat: I have not tested this, as I don't have Python 3.)