python dict append to list error(value with \)-CodePudding

I got a problem when appending a dict to list

    data = []
    path = "abc\cde"
    data.append({"image": path})
    print(data)

When I append the path to the image, the output of data is [{'image':'abc\def'}]. It contains two \ instead of one.

CodePudding user response：

\ is an escape character. It allows you to use special symbols, for example a new line \n or tab \t. If you want a string to contain a literal \, make sure that you put another \ before it.

In your case, Python understands that you meant "abc\\cde" even though you did not escape \. If you had abc\nde, the result would be abc<line_break>de.

>>> a = "abc\\cde"
>>> a
'abc\\cde'
>>> list(a)
['a', 'b', 'c', '\\', 'c', 'd', 'e']

As you see, even though it looks like a double backslash, it is just one \ character.

More info: https://www.w3schools.com/python/gloss_python_escape_characters.asp

CodePudding user response：

The additional backslash is Python escaping the single backslash. The actual value of your path string is unchanged, as you can see when the value of data[0]['image'] is printed.

data = []
path = 'abc\cde'
data.append({"image": path})

# output: abc\cde
print(data[0]['image'])

CodePudding user response：

When typing text that contains slashes, use raw strings to avoid having some sequences be interpreted as special characters, e.g. "\n" in a python string is a single character that represents a new line.

>>> data = []
>>> data.append({"image": r'abc\cde'})
>>> data
[{'image': 'abc\\cde'}]
>>>
>>> data.append({"image": r'abc\nasdf'})
>>> data
[{'image': 'abc\\cde'}, {'image': 'abc\\nasdf'}]

When you see two slashes is because that's how python repr-esents a string with slashes safely, it's not the actual content.

>>> r'abc\cde'
'abc\\cde'
>>> r'abc\nasdf'
'abc\\nasdf'

In this way a text with special chars can be visualized in a compact way. If you want to see what the actual content of those strings looks like, print them:

>>> print(r'abc\cde')
abc\cde
>>> print(r'abc\nasdf')
abc\nasdf
>>> print('abc\cde')
abc\cde
>>> print('abc\nasdf')
abc
asdf