Question

相关代码是：

while True:
    command = raw_input("Please enter a command: ")
    cls()
    if command == "quit":
        cls()
        quit()
        break
    if command == "add":
        cls()
        problem=add()
        cls()
        if problem==1:
            print "Invalid subject type! Check your spelling, or use the new subject command."
        if problem==2:
            print "Invalid problem type! Please use the *insert new type command here*."
        if problem==3:
            print "Invalid date! Check your spelling or try to express it in another way (i.e. 1/2/14, tomorrow, or in 3 days)."
        if problem==4:
            print "The time you entered was in the past! Hopefully you've already turned in that assignment!"
        if problem==5:
            print "Both the subject and the type are incorrect"
    if command == "print" or "optimize" or "list":
        cls()
        optimize_print()
    if command == "optimize":
        cls()
        optimize_print()
    if command == "remove":
        cls()
        if len(assignments) != 0:
            remove()
        else:
            print "There is nothing to remove"
        cls()
    if command == "open website":
        cls()
        site = raw_input("What website would you like to open? ")
        open_web(site)
    if command == "clear":
        certainty = raw_input("This action cannot be undone. Are you sure you want to clear all assignments? ")
        if "y" in certainty:
            clear_all()
        else:
            pass
    if command == "start" or "run":
        run_prog()
    if command == "new subject":
        cls()
        sub = raw_input("What subject would you like to add? ")
        for i in subjects:
            if sub.lower() == i.lower():
                print "That subject already exists."
                break
                break
            else:
                pass
        new_subject(sub)
    elif command == "change website" or "new website":
        cls()
        subject_to_add_website = raw_input("What subject would you like to add/change a website for? ")
        change_website(subject_to_add_website)
    if command == "new assignment" or command == "new type" or command == "new assignment type":
        cls()
        ty = raw_input("What assignment type would you like to add? ")
        for i in types:
            if ty.lower() == i.lower():
                print "That assignment type already exists."
                break
                break
            else:
                pass
        new_type(ty)

我们在python 2.7中有一个调度程序，一旦给定的函数运行完毕，它会使用while循环来提示输入新的输入。突然间没有我们意识到在while循环中发生了任何重大更改，程序现在执行所有if语句，即使您输入的字符串与其中任何一个都不匹配。我错过了一些明显的东西吗？（我应该补充说这是在控制台中运行并且以前工作但现在在各种mac和pc上都失败了）

Answer 1

包含or的所有if语句都会运行，无论command的值如何。这是因为字符串文字被评估为True

条件if command == "start" or "run"首先评估command的值，然后评估＆＃34;真实性＆＃34;字符串run。始终满足此条件，并始终运行其后的代码。

这应该改为：

if command == "start" or command =="run":
    do.something()

Answer 2

比较

command == "print" or "optimize" or "list"

将始终评估为True。 Python将其评估为

(command == "print") or bool("optimize") or bool("list") # non-empty strings evaluate to True

以下是更正代码的方法：

command == "print" or command == "optimize" or command == "list"

pythonic的写作方式是：

command in ("print", "optimize", "list")

Answer 3

而不是输入：

command == "start" or "run"

您应该输入：

command == "start" or command == "run"

因为在第一种情况下，或者＆＃34;运行＆＃34;将无条件地宣告为True，因此每次都会执行

Simple While True循环和if语句无法触发

3 个答案: