比較列表和文件以在python中進行匹配

Question

我想遍歷列表中的每個元素，並檢查該元素是否與文本文件中的任何產品匹配。 我已經做到了：

print("Opening a file")
pro_file = open("inventory.txt", "r")   #open text file for reading

#print(pro_file.read())    #read text file line by line
productList = ['chips', 'biscuits', 'pasta', 'cheese', 'bread', 'rice', 'honey', 'butter', 'cake', 'salt'];

for key in productList:
    for line in pro_file.readlines():
        if key in line:
            print("found" + key)

嵌套的for循環僅給出productList中第一項的匹配項。 我說過幾天前學習python，所以任何幫助將不勝感激。

Answer 1

第一次調用pro_file.readlines() ，您到達文件的末尾。 第二次調用時，沒有其他內容可供閱讀。

只需讀取一次文件：

with open("inventory.txt", "r") as f:
    pro_file = f.readlines()

然后循環pro_file列表

for key in productList:
    for line in pro_file:
        if key in line:
            print("found" + key)

---

但是，如果您只想知道其中之一

productList = ['chips', 'biscuits', 'pasta', 'cheese', 'bread', 'rice', 'honey', 'butter', 'cake', 'salt'];

在pro_file ，您不必關心它在哪里，可以通過以下方式簡化上述代碼：

for key in productList:
    if key in pro_file:
        print("found" + key)

Answer 2

問題在於，一旦您調用readlines（），文件的末尾就會到達，而下次您在同一個打開的文件上調用它時，它將不會返回任何內容。 一個快速的解決方法是將兩者換成這樣的語句：

for line in pro_file.readlines():
    for key in productList:

但是，這將對大文件造成問題，因為readlines（）在文件中創建了所有行的列表並將其存儲在內存中。 因此，您可以嘗試一下。 我添加了評論以解釋其他一些更改。

# Per PEP8, variable names should be all lower case with underscores between words
product_list = ['chips', 'biscuits', 'pasta', 'cheese', 'bread', 'rice', 'honey', 'butter', 'cake', 'salt'];

# This is a context manager. It will ensure the file is closed when the code block is finished
# No need to include 'r' when opening a text file as read-only. It's the default.
with open("inventory.txt") as pro_file:
    for this_line in pro_file:
        # A text file can be iterated through one line at a time this way, without loading everything into memory
        for product in product_list:
            if product in this_line:
                # Using format is cleaner and easier to read than + and will work even if the value is a number
                print('Found: {}'.format(product))
                # Since you found a product, you can stop checking products. Break will stop the for product loop.
                break
        else:  # no break
            # What the heck is this? An else in a for loop?
            # In Python, this means "do this if you didn't hit a break statement," and it's very useful.
            # I usually add the comment "no break" after it so it's a little more clear that it was intentional.
            print('Did not find any products in this line')