Crypto Mentorship: Caesar Cipher

caeser_cipher.py

# To run the file: python3 file_name method_flag (either 1:brute force or 2:frequency analysis)
import sys
cipher=open("cipher.txt","r")
lines=[]
for line in cipher:
    lines.append(line)

if(int(sys.argv[1])==1):
    #Try shifting and printing
    while(True):
        shift=int(input("Enter the shift: "))
        for line in lines:
            l=[]
            for char in line:
                if(ord(char)>=ord("a") and ord(char) <= ord("z") ):
                    l.append(chr( ( ( ord(char)-ord('a') )+shift )%26 +ord('a') ))
                else:
                    l.append(char)
            l=''.join(map(str, l))
            print(l)

else:
#By frequency analysis
    freq=[0 for _ in range(26)]
    alphaCount=0
    for line in lines:
        l=[]
        for char in line:
            if(ord(char)>=ord("a") and ord(char) <= ord("z") ):
                alphaCount+=1
                freq[ord(char)-ord("a")]+=1
    for i in range(26):
        print((chr(ord("a")+i)),":",(freq[i]/alphaCount)*100)