Python - remove specific line in string variable

Question

Is it possible in Python to remove only single line from a string variable without doing the concatenation of both chunks? I'm after removing cachedLength line.

input_columns = f'''\
<inputColumn 
    refId="Package\DFT\DST.Inputs[DST Input].Columns[{tbl}]"
    cachedDataType="{dt_type}"
    cachedName="{tbl}"
    cachedLength="{dt_lngh}"
    cachedPrecision="{dt_prc}"
    cachedScale="{dt_scl}"
    externalMetadataColumnId="Package\DFT\DST.Inputs[DST Input].ExternalColumns[{tbl}]"
    lineageId="Package\DFT\SRC.Outputs[SRC Output].Columns[{tbl}]" />
'''

Work in progress:

i = input_columns.split("\n")[4]
print(input_columns.replace(i, ""))

Not possible. Strings are immutable in Python. Use str.replace or re.sub to create new string instead. — wim
– wim, Commented Sep 21, 2021 at 21:34
Your choices are usually: split and rejoin the string, replace a fixed substring with string.replace(), replace with re.sub(), or use a library to manage a particular kind of data (HTML, XML, etc.). — sj95126
– sj95126, Commented Sep 21, 2021 at 21:36
You can use a combination of str.split and str.join, but I think that would be "concatenating" again. — tdelaney
– tdelaney, Commented Sep 21, 2021 at 21:42
What you have is an XML element. You shouldn't be trying to remove lines from an arbitrarily formatted string; you should parse it, remove an attribute, and reserialize the result. — chepner
– chepner, Commented Sep 21, 2021 at 21:43
To be specific, this is XML/DTSX file I need to modify data for. I know there is BIML/EzAPI but they don't support Python. — marcin2x4
– marcin2x4, Commented Sep 21, 2021 at 21:52

Yann · Accepted Answer · 2021-09-21 22:00:40Z

1

You can replace the line using re module:

re.sub(r'\s*cachedLength=".*"', '', input_columns)

But as mentioned in the comments, technically, Python will recreate the string because it's an immutable type.

answered Sep 21, 2021 at 22:00

Yann

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onepan · Accepted Answer · 2021-09-23 16:48:53Z

1

Not exactly answering the question, but if modifying the xml is what you're after, you could use a package for that. E.g., using lxml:

from lxml import etree

xml = """\
<inputColumn 
    refId="Package\DFT\DST.Inputs[DST Input].Columns[{tbl}]"
    cachedDataType="{dt_type}"
    cachedName="{tbl}"
    cachedLength="{dt_lngh}"
    cachedPrecision="{dt_prc}"
    cachedScale="{dt_scl}"
    externalMetadataColumnId="Package\DFT\DST.Inputs[DST Input].ExternalColumns[{tbl}]"
    lineageId="Package\DFT\SRC.Outputs[SRC Output].Columns[{tbl}]" />
"""

e = etree.fromstring(xml)

del e.attrib["cachedLength"]

print(etree.tostring(e, pretty_print=True, encoding="unicode"))

edited Sep 23, 2021 at 16:48

answered Sep 21, 2021 at 22:29

onepan

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