为什么我的 Python 正则表达式与 Windows 中的换行符 \\r\\n 不匹配？

Question

I'm still fairly new to Python, and am having trouble with one of my regular expressions. I've researched this online and tried lots of things in Python, but am stuck. Since I'm using Windows, I'm expecting \\r\\n to match a new line break in a text file because that's how lines are terminated in Windows. But what I'm finding is that only \\n matches. Why is that?

Here's my code (using \\r\\n, which doesn't match)

filename = 'C:\\Users\\jason\\OneDrive\\Documents\\LTspice_my_work\\example_ac_analysis_2.raw'
with open (filename, 'r' ) as f:
    content = f.read()
    print(content)
    pattern3 = r'Variables:\r\n(.*)Values:' 
    print("Here's what matches:")
    text = re.search( pattern3,content,re.DOTALL).group(1)
    print(text)

which returns:

Command: Linear Technology Corporation LTspice XVII
Variables:
        0       frequency       frequency
        1       V(v1)   voltage
        2       V(vout) voltage
        3       I(C1)   device_current
        4       I(R1)   device_current
        5       I(V1)   device_current
Values:
0               1.000000000000000e+000,0.000000000000000e+000
        2.000000000000000e+000,0.000000000000000e+000
        1.998028025380720e+000,-6.276990166202591e-002
        3.943949238559487e-007,1.255398033240518e-005
        -3.943949238559341e-007,-1.255398033240518e-005
        -3.943949238559568e-007,-1.255398033240518e-005
1               3.162277660168380e+000,0.000000000000000e+000
        2.000000000000000e+000,0.000000000000000e+000
        1.980453705393099e+000,-1.967499214255068e-001
        3.909258921380289e-006,3.934998428510137e-005
        -3.909258921380277e-006,-3.934998428510137e-005
        -3.909258921380287e-006,-3.934998428510137e-005


Here's what matches:
Traceback (most recent call last):

  File "C:\Users\jason\OneDrive\Documents\Python\Python_scripts\example_ltspice_pytool.py", line 176, in <module>
    text = re.search( pattern3,content,re.DOTALL).group(1)

AttributeError: 'NoneType' object has no attribute 'group'

But when I use only \\n I get the match I'm looking for with this code

filename = 'C:\\Users\\jason\\OneDrive\\Documents\\LTspice_my_work\\example_ac_analysis_2.raw'
with open (filename, 'r' ) as f:
    content = f.read()
    print(content)
    pattern3 = r'Variables:\n(.*)Values:' 
    print("Here's what matches:")
    text = re.search( pattern3,content,re.DOTALL).group(1)
    print(text)

which returns

Command: Linear Technology Corporation LTspice XVII
Variables:
        0       frequency       frequency
        1       V(v1)   voltage
        2       V(vout) voltage
        3       I(C1)   device_current
        4       I(R1)   device_current
        5       I(V1)   device_current
Values:
0               1.000000000000000e+000,0.000000000000000e+000
        2.000000000000000e+000,0.000000000000000e+000
        1.998028025380720e+000,-6.276990166202591e-002
        3.943949238559487e-007,1.255398033240518e-005
        -3.943949238559341e-007,-1.255398033240518e-005
        -3.943949238559568e-007,-1.255398033240518e-005
1               3.162277660168380e+000,0.000000000000000e+000
        2.000000000000000e+000,0.000000000000000e+000
        1.980453705393099e+000,-1.967499214255068e-001
        3.909258921380289e-006,3.934998428510137e-005
        -3.909258921380277e-006,-3.934998428510137e-005
        -3.909258921380287e-006,-3.934998428510137e-005


Here's what matches:
        0       frequency       frequency
        1       V(v1)   voltage
        2       V(vout) voltage
        3       I(C1)   device_current
        4       I(R1)   device_current
        5       I(V1)   device_current

Thanks for your help in advance!

Answer 1

当您以文本模式（默认）打开文件时， \\r\\n会在您读取文件时自动转换为\\n ，因此您不必担心您使用的是什么操作系统。

Answer 2

Python, by default, processes text files in universal newline mode. Quoting from the docs :

newline controls how line endings are handled. It can be None , '' , '\\n' , '\\r' , and '\\r\\n' . It works as follows:

• When reading input from the stream, if newline is None , universal newlines mode is enabled. Lines in the input can end in '\\n' , '\\r' , or '\\r\\n' , and these are translated into '\\n' before being returned to the caller. If it is '' , universal newlines mode is enabled, but line endings are returned to the caller untranslated. If it has any of the other legal values, input lines are only terminated by the given string, and the line ending is returned to the caller untranslated.

So in short, your strings don't have \\r in them by the time you receive them. If you want them to keep the \\r , change your open call to add newline='' (the csv module requires this, because line-endings are part of the CSV dialect, and it needs the original, untranslated endings to process the input correctly).