How do I read a text file in python via PowerShell? Windows 10

Question

I'm having problems reading text files into my python programs.

import sys

words = sys.stdin.readlines()

I'm reading the file in through stdin but when I try to execute the program I'm getting this error.

PS> python evil_61.py < evilwords.txt

At line:1 char:19
+ python evil_61.py < evilwords.txt
+                   ~

The '<' operator is reserved for future use.
    + CategoryInfo          : ParserError: (:) [], ParentContainsErrorRecordException
    + FullyQualifiedErrorId : RedirectionNotSupported

Could someone tell me how to run these kinds of programs as it is essential for my course and I'd rather use Windows than Linux.

Answer 1

Since < for input redirection is not supported in PowerShell, use Get-Content in a pipeline instead:

Get-Content evilwords.txt | python evil_61.py 

^{Note: Adding the -Raw switch - which reads a file as a single, multi-line string - would speed things up in principle (at the expense of increased memory consumption), but PowerShell invariably appends a newline to data piped to external programs, as of PowerShell 7.2 (see this answer), so the target program will typically see an extra, empty line at the end. Get-Content's default behavior of line-by-line streaming avoids that.}

Beware character-encoding issues:

• Get-Content, in the absence of an -Encoding argument, assumes the following encoding:

  • Windows PowerShell (the built-into-Windows edition whose latest and final version is 5.1): the active ANSI code page, which is implied by the active legacy system locale (language for non-Unicode programs).
  • PowerShell (Core) 7+: (BOM-less) UTF-8

• On passing the lines through the pipeline, they are (re-)encoded based on the encoding stored in the $OutputEncoding preference variable, which defaults to:

  • Windows PowerShell: ASCII(!)
  • PowerShell (Core) 7+: (BOM-less) UTF-8

As you can see, only PowerShell (Core) 7+ exhibits consistent behavior, though, unfortunately, as of PowerShell Core 7.2.0-preview.9, this doesn't yet extend to capturing output from external programs, because the encoding that controls the interpretation of received data, stored in [Console]::OutputEncoding], still defaults to the system's active OEM code page - see GitHub issue #7233.

Answer 2

Consider passing the text file as an argument at command line for Python script to use. All command line arguments (including file name) come stored in the sys.argv list:

Python Script (in evil_61.py)

import sys

txtfile = sys.argv[1]
with open(txtfile) as f:
    content = f.readlines()

PowerShell Command

PS> python evil_61.py evilwords.txt

Answer 3

Because the '<' is interpreted by the PowerShell engine as redirection operator.

Quit PowerShell for your Python stuff and hop on to cmd or cygwin. Based on the context of this question, I see no reason why you should use escape characters for the sake of using PowerShell as CLI to learn Python.