为什么 read().split("\n") 会导致错误，即使它从列表中删除了 "\n" 不像 readlines() 和 readlines() 工作

Question

File1 contains the following integers:

3
6
5
8
33
12
7
4
72
2
42
13

File2 contains the following integers:

3
6
13
5
7
89
12
3
33
34
1
344
42

Error for read()split("n")

    Traceback (most recent call last):
      File "main.py", line 12, in <module>
        result = [int(number) for number in list1 if number in list2]
      File "main.py", line 12, in <listcomp>
        result = [int(number) for number in list1 if number in list2]
    ValueError: invalid literal for int() with base 10: ''

Output for: Question: Why does this section of code work when the other does not? I figured I had to removed the "\n" from the newly created strings in the list1 and list2 before it could be converted into an integer using the list comprehension, which is why I tried the read().split("\n") code section first to remove the escape character. The readlines() section of code is able to convert the strings containing "\n" no problem. Is this because when using the int() escape characters are ignored?

    with open("file1.txt","r") as file1:
          #list1 = file1.readlines()
    with open("file2.txt","r") as file2:
          list2 = file2.readlines()

['3\n', '6\n', '5\n', '8\n', '33\n', '12\n', '7\n', '4\n', '72\n', '2\n', '42\n', '13\n']

['3\n', '6\n', '13\n', '5\n', '7\n', '89\n', '12\n', '3\n', '33\n', '34\n', '1\n', '344\n', '42\n']

[3, 6, 5, 33, 12, 7, 42, 13]

Python:

with open("file1.txt","r") as file1:
    list1 = file1.read().split("\n")
with open("file2.txt","r") as file2:
    list2 = file2.read().split("\n")

# with open("file1.txt","r") as file1:
      #list1 = file1.readlines()

# with open("file2.txt","r") as file2:
      #list2 = file2.readlines()

result = [int(number) for number in list1 if number in list2]

print(result)

Answer 1

It's a little unclear what you are asking but I'll do my best to answer why these two lines are not equivalent and why the second one leads to a ValueError .

• file1.readlines()
• file1.read().split("\n")

file1.readlines()

This one is simple. The readlines method simply converts a file into a list of strings. One line in the file corresponds to one item in the list. There are 12 rows in the file so you get a list of 12 strings.

with open("file1.txt", "r") as file1:
    print(file1.readlines())

# ['3', '6', '5', '8', '33', '12', '7', '4', '72', '2', '42', '13']

file1.read().split("\n")

The read method returns the entire file as a string, in this case. This also includes newline characters as you noted in the original post.

with open("file1.txt", "r") as file1:
    file1.read()

# '3\n6\n5\n8\n33\n12\n7\n4\n72\n2\n42\n13\n'

Now when you use the split method on a string, it Python splits the string at instance of the delimiter and returns all pieces of the string. For example, if I say "123".split("2") then I can expect ['1', '3'] to be returned. However, it's less intuitive what happens when the specified delimiter is at the end of the string. If I say "123".split("3") then I can expect ['12', ''] . So if the delimiter is at the end or beginning of a string, split will return an empty string at the end or beginning of the list.

In the case of file1 , there is a \n delimiter at the end of the string so you can expect something like this when split:

with open("file1.txt", "r") as file1:
    file1.read().split('\n')

# ['3', '6', '5', '8', '33', '12', '7', '4', '72', '2', '42', '13', '']

So when you try to cast the last item in the list ( '' ) to an int , you get ValueError: invalid literal for int() with base 10: '' .

Bonus: file1.read().splitlines()

Another option is the splitlines method which will split on newlines but strip any leading or trailing whitespace.

with open("file1.txt", "r") as file1:
    file1.read().splitlines()

# ['3', '6', '5', '8', '33', '12', '7', '4', '72', '2', '42', '13']