numpy=1.14
 pandas=1.4
 django=1.6
 flask=1.4

import sys
 import re
 program_name = sys.argv[0]
 arguments = sys.argv[1:]
 print (arguments[0])
 print (arguments[1])
 with open('requirement.txt ', 'r') as fr:
     data = fr.readlines()
     with open('requirement.txt ', 'a') as fw:
     fw.write(....)

numpy=1.14
 pandas=1.4
 django=2.1
 flask=2.0

import re
import sys

arguments = dict(i.split("=") for i in sys.argv[1:])   #CMD line Arguments.
with open('requirement.txt', 'r') as fr:         #Read content
    data = fr.read()

for k, v in arguments.items():
    data = re.sub(r"{}=(.*)".format(k), "{}={}".format(k,v), data)   #Update content

with open(filename, 'w') as fr:              #Write back data.
    fr.write(data)

import sys

requirements = {}

# Save a list of requirements
with open('requirement.txt', 'r') as file:
  for line in file:
    line = line.strip("n").split("=")
    requirements[line[0]] = line[1]

# Change requirements values
for command in sys.argv[1:]:
  command = command.split("=")
  requirements[command[0]] = command[1]

# Write requirements back to file
with open('requirement.txt', 'w') as file:
  for r, v in requirements.items():
    line = "{}={}n".format(r, v)
    file.write(line)

import sys
import fileinput

program_name = sys.argv[0]
args = sys.argv[1:]

if not args:    # ensuring replacement items were passed
    sys.exit('No items to replace')

args_dict = dict(arg.split('=') for arg in args)
keys_tuple = tuple(args_dict.keys())

for line in fileinput.input(files='requirements.txt', inplace=True):
    if line.startswith(keys_tuple):
        name, version = line.split('=')
        line = line.replace(version, args_dict[name])
    print(line.strip())

numpy=1.14
pandas=1.4
django=2.1
flask=2.0

numpy=1.14
pandas=1.4
django=1.6
flask=1.4
django=2.1
flask=2.0

fr=open('requirement.txt ', 'r')
L=fr.read().split("n") #Better than .readlines(), since it removes 'n'
fr.close() #Very important, since you're going to write back into it.
D=dict()
for e in L:
    E=e.split("=")
    if len(E)<2:
        continue
    D[E[0]]=E[1]

D[arguments[0]]=arguments[1]

result="n".join([e+"="+D[e] for e in D])
fw=open('requirement.txt ', 'a')
fw.write(result)
fw.close()