在Python中检查项是否在集合中？

Question

编写一个程序来检查用户输入的单词是否在预先存在的集合中；无论我输入什么单词，程序都返回“False”（即使是我知道的单词在集合中）。代码如下：

name = input("which file would you like to open?  ")
s=input("word?  ")

F = open(name, "r")
words = set()
words.add(F)

def contains(s,words):
    if s in words:
        print("true")
    else:
        print("false")
contains(s,words)

Answer 1

正确的方法是使用发电机：

name = input("which file would you like to open?  ")
word_to_look_for=input("word?  ")

def check(word_to_look_for, word_from_file):
    return word_to_look_for == word_from_file

with open(name, "r") as file:
    # The code inside the parentheses () returns a generator object
    word_exists = (check(word_to_look_for, word_from_file.rstrip("\n")) for word_from_file in file.readlines())  

# This will return true if either one of the "check" function results is True 
print(any(word_exists))

Answer 2

假设文件中每行有一个单词，例如

asd
asdf

您可以使用它，它将每一行添加到words：

name = input("which file would you like to open?  ")
s = input("word?  ")

F = open(name, "r")
words = set()
for line in F:  # add every line to words (assuming one word per line)
    words.add(line.strip())

def contains(s, words):
    if s in words:
        print("true")
    else:
        print("false")

contains(s, words)

打印输出：

which file would you like to open?  file.txt
word?  asd
true

---

编辑：对于实际任务来说，这是一种更短的方法：

name = input("which file would you like to open?  ")
s = input("word?  ")

F = open(name, "r")
print("true") if s in F.read() else print("false")

Answer 3

假设您的文件如下所示：

banana
apple
apple
orange

让我们创建该文件：

with open("test.txt","w") as f:
    f.write("banana\napple\napple\norange")

现在让我们运行一个示例代码：

s= input("word?  ")

words = set()

# Using with we don't need to close the file
with open("test.txt") as f:
    # here is the difference from your code
    for item in f.read().split("\n"):
        words.add(item)

def contains(s,words):
    for word in words:
        if s in word:
            print("true")
            break
    else:
        print("false")

contains(s,words)

键入：

apple returns "true"

ap returns "true"

oeoe returns "false"