在python中比较匹配的列表和文件

我想循环列表中的每个元素，并检查该元素是否与文本文件中的任何产品匹配。我已经这样做了：

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循环仅提供productList中第一项的匹配。几天前我已经说过要学习python，所以如果有任何帮助，我们将不胜感激。

第一次调用

pro\u file.readlines（）

，您将看到文件的末尾。第二次你叫它的时候，就没什么可读的了

只需读取一次文件：

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

然后循环

pro_文件

列表

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

---

但是如果你只是想知道

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

在

pro_文件中

并且您不关心它在哪里，您可以通过以下方式简化上述代码：

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

---

第一次调用

pro\u file.readlines（）

，您将到达文件的末尾。第二次你叫它的时候，就没什么可读的了

只需读取一次文件：

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

然后循环

pro_文件

列表

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

---

但是如果你只是想知道

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

在

pro_文件中

并且您不关心它在哪里，您可以通过以下方式简化上述代码：

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

---

问题是，一旦调用readlines（），就到达了文件的结尾，下次在同一个打开的文件上调用它时，它将不会返回任何内容。一个快速解决方法是将这两个语句交换为如下语句：

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

但是，对于大文件，这会有问题，因为readlines（）会创建文件中所有行的列表并将其存储在内存中。所以，你可以试试这个。我添加了一些注释来解释其他一些更改

# 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')

---

问题是，一旦调用readlines（），就到达了文件的结尾，下次在同一个打开的文件上调用它时，它将不会返回任何内容。一个快速解决方法是将这两个语句交换为如下语句：

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

但是，对于大文件，这会有问题，因为readlines（）会创建文件中所有行的列表并将其存储在内存中。所以，你可以试试这个。我添加了一些注释来解释其他一些更改

# 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')

---

您应该将

的顺序替换为
循环。您应该将
的顺序替换为
循环。