import csv
def gen(csv_f):
    # var define
    for row in csv.DictReader(open(csv_f)):
        c += row['x']
        ...
    a  = 1
    b  = 2
    ...
    # do sth in f0
    xx = a + b
    ...
    str = ...
    return str

import csv
def gen(csv_f):
    # var define
    for row in csv.DictReader(open(csv_f)):
        c += row['x']
        ...
    a  = 1
    b  = 2
    ...
    # do sth in f1
    xx = a*b + b
    ...
    str = ...
    return str

from f0 import *
from f1 import *

f = open('xxx.x','w')
f.write(f0.gen(1)+f1.gen(1))
f.close()

class conf:
    def __init__(self, csv_f):
        # var define
        for row in csv.DictReader(open(csv_f)):
            c += row['x']
            ...
        self.a  = 1
        self.b  = 2
        ...

import conf
class f0(conf):
    def __init__(self):
        config.__init__(self, csv_f) #this line is not correct
    def gen():
        # var set
        c = self.c
        a = self.a
        b = self.b
        # do sth in f0
        xx = a + b
        ...
        str = ...
        return str

import conf
class f1(conf):
    def __init__(self):
        config.__init__(self, csv_f) #this line is not correct
    def gen():
        # var set
        c = self.c
        a = self.a
        b = self.b
        # do sth in f1
        xx = a + b
        ...
        str = ...
        return str

from f0 import *
from f1 import *

f = open('xxx.x','w')
f.write(f0.gen(1)+f1.gen(1))
f.close()

for row in csv.DictReader(open(csv_f)):
    c += row['x']

import conf
class f0(conf):
    def __init__(self, csv_f):
         super(f0,self).__init__(self)  # Fixed
         self.csv_f = csv_f

    def gen(self):
         # var set
         c = self.c #
         a = self.a
         b = self.b
         # do sth in f0
         xx = a + b

from f0 import *
from f1 import *

f = open('xxx.x','w')
f.write(f0(filename).gen()+f1(filename).gen())
f.close()

xx = a + b

xx = a*b + b

def gen(csv_f, f):
    # var define
    for row in csv.DictReader(open(csv_f)):
        c += row['x']
        ...
    a  = 1
    b  = 2
    ...
    # use the passed function
    xx = f(a, b)
    ...
    return str

l0 = lambda a, b: a + b
l1 = lambda a, b: a * b + b

# call gen with one of these lambdas as the second argument
gen(1, l0)
gen(1, l1)