Code Snippet

#ALTERNATIVE METHOD that does not use f.readlines()

"""
 f.readlines() does not handle the \n occurrences
We can simply iterate through the file object to get each line, this will give us
each line with the \n characters already stripped, and is the more pythonic implementation
for this use case. As such, we can use the following solution with list comprehension;

"""
"""File contents
Mr Moose : Maths
Mr Goose: History
Mrs Cook: English

"""

alldata=[]
col_num=0
teacher_names=[]
delimiter=":"

def main():
      with open("teacherbook.txt") as f:
            #getting each line with \n stripped and removing the blank spaces
            alldata = [':'.join([value.strip() for value in line.split(':')]) 
               for line in f]
            print(alldata)

            print()
            print()

            for x in alldata: 
                   teacher_names.append(x.split(delimiter)[col_num].strip()) 


            teacher=input("Enter teacher you are looking for:")
            if teacher in teacher_names: 
                  print("Yes, that teacher exists")
            else:
                  print("Nope, not found")

main()
                    

Try it yourself