“NameError：名称未定义”是什么意思？

Question

So I've been working on my text encryption and decryption program, and I am stuck. This is what I have so far:

  import random
  def fileopen():
       filename=input("What is the file you need to encrypt:")
       print(filename)
       with open(filename) as wordfile:
             contents=wordfile.read()
       return contents
 def Create8():
      numlist=[]
      charlist=[]
      for i in range (8):
           num=random.randint(33,126)
           numlist.append(num)
 for i in numlist:
      char = chr(i)
      charlist.append(char)
      return charlist
 def offset(key):
  store=[]
  for i in key:
        num=ord(i)
        store.append(num)
  total=sum(store)
  oFactor=((total//8)-32)

  return oFactor



  while True:
       print ("Hello, welcome to the encryption/decryption program")
       print ("1 - Encryption")
       print ("2 - Decryption")
       print ("3 - Exit")
       choice=input ("Enter a Number")

  if choice=="1":
       print("Encryption Selected")

       contents=fileopen()
       print(contents)

       Characterkey=Create8()

        OF=offset(Characterkey)

        print ("The offset factor is:")
        print (OF)

        Etext=[]
        for i in contents:
            if i ==" ":
                Etext.append(i)
            else:
                code=ord(i)
                code=code+OF
                if code >126:
                    code=code-94
                char=chr(code)
                Etext.append(char)
        print(Etext)
        encryptedtext=(''.join(Etext))
        print(''.join(Etext))

        filename=input ("What is your file going to be called")

        with open(filename,"w")as f:
              f.write(encryptedtext)

        continue


        def decrypt():
              file = input("""Please enter the name of your text file to be decrypted:
             """)
        if not file.endswith('.txt'):
              file+='.txt'
        try:
              with open (file, 'r') as file:
                    texts= file.read()
        except IOError:
              print("Error- please try again")


  character_key= input ("\nPlease enter the EXACT eight character key that was used to encrypt the message: ")

  offsetfactor_decrypt = sum(map(ord, character_key))//8-32
  result =  ''
  for letter in text:
              if letter == " ":
                    result += " "
  else:
        n = ord(letter) - offsetfactor_decrypt
        if n <33:
              n = n+ 94
              result = result + chr(n)

  print ("\nHere is your decrypted text: \n",result,)

The problem I am having is this is displayed every time I run it:

Traceback (most recent call last):
  File "C:\Users\Callum Bowyer\Desktop\Text Encryption\Project2.py", line 105, in <module>
    for letter in text:
NameError: name 'text' is not defined

Answer 1

Your code is badly and ineffectively written and really badly indented (indentation in python is very important and if your code is not indented correctly you will get syntax error and not be able to execute that code, see http://www.python-course.eu/python3_blocks.php ). So i tried to fix your code as much as possible:

• first to even run your code I needed to fix indentation in hole program,
• then I put spaces around operators (+, -, =... signs), your program would work without this, but it much easier to read and try to understand code that is nicely written,

• after that i ran your code and tried to find out where is the problem, these are things that I changed in your code:

  • you already used

    if not file.endswith('.txt'): file += '.txt'`

    to check if name of text file to be decrypted has '.txt' extension, so I added same code to also check if name of text file to be encrypted and name of text file where encrypted text would be saved have '.txt' extensions,

  • a after block of code that executes if choice == "1": I added elif choice == "2": and put all code from decrypt() function after that elif statement,

  • I added another elif statement

    elif choice == "3": break

    so when user enters 3 program stops executing,

  • your functions Create8() and offset(key) are ineffective, first in function Create8() you create numlist from which than you create charlist and from function Create8() you return charlist , after that you call function offset(key) where argument key is charlist returned from function Create8() , in function offset(key) you create store which is identical to numlist from function Create8() , so to make your code effective I merged functions Create8() and offset(key) to one function Create8_and_offset()

     def Create8_and_offset(): charlist=[] total = 0 for i in range(8): num = random.randint(33,126) total += num char = chr(num) charlist.append(char) oFactor = (total//8 - 32) return charlist, oFactor

  • and finally the reason why your code raises NameError is ( Nullman , nexus66 and zaph have mentioned it in comments) that instead of non-existing variable text that you use you should use variable texts , you should use this:

     for letter in texts:

    instead of this:

     for letter in text:

Full (fixed) code that works:

import random


def fileopen():
    filename = input("What is the file you need to encrypt: ")
    if not filename.endswith('.txt'):       # this was added to check
        filename += '.txt'                  # that file has .txt extension
    print(filename)
    with open(filename) as wordfile:
        contents = wordfile.read()
    return contents


def Create8_and_offset():
    charlist=[]
    total = 0
    for i in range(8):
        num = random.randint(33,126)
        total += num
        char = chr(num)
        charlist.append(char)
    oFactor = (total//8 - 32)
    return charlist, oFactor


##def Create8():
##    numlist=[]
##    charlist=[]
##    for i in range (8):
##        num=random.randint(33,126)
##        numlist.append(num)
##    for i in numlist:
##        char = chr(i)
##        charlist.append(char)
##    return charlist
##
##def offset(key):
##    store=[]
##    for i in key:
##        num=ord(i)
##        store.append(num)
##    total=sum(store)
##    oFactor=((total//8)-32)
##    return oFactor



while True:
    print("Hello, welcome to the encryption/decryption program")
    print("1 - Encryption")
    print("2 - Decryption")
    print("3 - Exit")
    choice = input("Enter a Number: ")

    if choice == "1":
        print("Encryption Selected")
        contents = fileopen()
        print(contents)
        #Characterkey = Create8()
        #OF = offset(Characterkey)
        Characterkey, OF = Create8_and_offset()
        print("The Characterkey is:\n" + ''.join(Characterkey))
        print("The offset factor is:")
        print(OF)

        Etext=[]
        for i in contents:
            if i == " ":
                Etext.append(i)
            else:
                code = ord(i)
                code = code + OF
                if code > 126:
                    code = code - 94
                char = chr(code)
                Etext.append(char)
        print(Etext)
        encryptedtext = (''.join(Etext))
        print(encryptedtext)

        filename = input("What is your file going to be called: ")
        if not filename.endswith('.txt'):       # this was added to check
            filename += '.txt'                  # that file has .txt extension

        with open(filename,"w")as f:
            f.write(encryptedtext)

        #continue

    elif choice == "2":

    #def decrypt():
        file = input("Please enter the name of your text file to be decrypted:\n")
        if not file.endswith('.txt'):
            file += '.txt'
        try:
            with open (file, 'r') as file:
                texts = file.read()
        except IOError:
            print("Error- please try again")


        character_key = input("\nPlease enter the EXACT eight character key that was used to encrypt the message: ")

        offsetfactor_decrypt = sum(map(ord, character_key))//8-32
        result =  ''
        #for letter in text:
        for letter in texts:
            if letter == " ":
            result += " "
            else:
                n = ord(letter) - offsetfactor_decrypt
                if n < 33:
                    n = n + 94
                result += chr(n)

        print ("\nHere is your decrypted text: \n", result)

    elif choice == "3":
        break

Answer 2

My suggestion would be to read a python introduction pdf. Your code has all kinds of errors over it. Studying python basics will help you a lot. Try getting to know more of functions and loops.