如何让 python 只读取文本文件的内容一次

Question

I am trying to figure out how to get Python to only read the contents of a.txt file once. It is for a class project to encrypt and decrypt a message using all printable ASCII characters. Doing it this way is not required. This is only my fourth program I have written in Python and I really don't know what I am doing but I enjoy trying to come up with different ways to approach assignments. I hope I have entered everything correctly on here. I know this an easy fix, I just haven't been able to find the answer. The assignment will be an ongoing project for the next 6 weeks. My plan is to make the encryption much more complex (yes I know that you should never use Python for encryption). So I am writing it with a bigger picture in mind.

That being said. If anyone wants to go beyond answering my question, feel free to tear the entire thing apart. Let me know what I've done wrong, why, how I could do it better. I would love to get some feedback.

import random
print("1. Encrypt")
print("2. Decrypt")
print(" ")

selection = int(input("What would you like to do? [1,2]? "))

while selection == 1:
    plainText = input('Enter the message you wish to encrypt: ')

    # right now the program encrypts the string at random between 1 and 95.  
    # All of the printable ASCII characters.
    # the code below is written for when I can take the parameters of 1-95
    # off and any input will simply loop around.
    distance = random.randint(1, 95)
    if distance < 1 or distance > 95:
        print('Try Again')
        continue
    else:

        # saves the random integer or (key) 
        # directly to a file without the user seeing it.

        f = open('..\\Desktop\\encryptPractice\\theKey.txt', 'w+')

        for key in range(1):
            number = distance
            f.write(str(number))

        f.close()

        code = ""

        for ch in plainText:
            ordvalue = ord(ch)
            ordvalue = ordvalue + distance

            while ordvalue < 32:
                ordvalue += 95
            while ordvalue > 126:
                ordvalue -= 95

            code += chr(ordvalue)

            # saves the encrypted message 
            # directly to a file without the user seeing it.

        f = open('..\\Desktop\\encryptPractice\\theMessage.txt', 'w+')

        for theMessage in range(1):
            secret = code
            f.write(str(secret))
        f.close()

        print('Your message has been saved to the file named theMessage.txt')
        break


# This is the decryption block - OPTION 
# 2.)*********************************************

while selection == 2:

    """
    I want to simply be able to open the file with the 'encrypted'
    message on it and then open the file with the 'key' on it and
    have the program decrypt the message and save it back to the
    same file.

    Both of the solutions below cause the program to read the
    'encrypted' message over and over and over and...you get it.
    """

    f = open('..Desktop\\encryptPractice\\theMessage.txt','r')
    for line in f:
        print(line)


    f = open('..Desktop\\encryptPractice\\theMessage.txt','r')
    while True:
        line = f.readline()
        if line == ""
            break
        print(line)

Answer 1

It's hard to understand your code because it's not indented properly. But here's my guess: the lines while selection == 1: and while selection == 2: make the block of code run in a loop until the value of selection changes. If think you are looking for if selection == 1: and if selection == 2: .

Now a couple other comments about the code you shared:

• It's impossible for distance to be less than 1 or more than 95 because randint(1, 95) returns an integer in the range [1, 95].

distance = random.randint(1, 95)
if distance < 1 or distance > 95:                                   
    print('Try Again')                                              
    continue

• You are using a for loop that iterates over a sequence of size 1 ( range(1) ):

for theMessage in range(1):
    secret = code
    f.write(str(secret))

This block can be reduced to f.write(str(code))