I'm working on Windows. I've a Python file to create a new CSV file and I view that using Notepad (even through Microsoft Excel).
import csv
data = [['fruit','quantity'], ['apple',5], ['banana',7],['mango',8]]
with open('d:\lineter.csv', 'w') as l:
w = csv.writer(l,delimiter='|', lineterminator='\r')
w.writerows(data)
The resulting file in Notepad:
fruit|quantityapple|5banana|7mango|8
Does the carriage return \r work or not? It works like lineterminator='' in Notepad. But in Excel, it works like '\n'.
The output doesn't seem to implement carriage return. When I use lineterminator as:
w = csv.writer(l, delimiter='|', lineterminator='*\r*\n')
The output in Notepad is:
fruit|quantity**
apple|5**
banana|7**
mango|8**
This is evident here too.
How does '\r' work in lineterminator in writer()?
Or is there another thing happening there?
The shorter answer:
When to use carriage return (CR, \r) vs. line feed (LF, \n) vs. both (CRLF, \r\n) to make a new line appear in a text editor on Windows, Mac, and Linux:
How does '\r' work in lineterminator in writer()??
It works fine in csv.writer(). This really isn't a Python, CSV, or writer problem. This is an operating system historical difference (actually, it's more accurate to state it is a program-specific difference) going back to the 1960s or so.
Or is there another thing happening there?
Yes, this is the one.
Your version of Notepad doesn't recognize a carriage return (\r) as a character used to display new lines, and hence won't display it as such in Notepad. Other text editors, such as Sublime Text 3, however probably would, even on Windows.
Up until about the year 2018 or so, Windows and Notepad required a carriage return + line feed (\r\n) together to display a new line. Contrast this to Mac and Linux, which require only \n.
The solution is to use \r\n for a new line on Windows, and \n alone for a new line on Mac or Linux. You can also try a different text editor, such as Sublime Text, when viewing or editing text files, or upgrade your version of Windows or Notepad, if possible, as somewhere around the year 2018 Windows Notepad started to accept \r alone as a valid old-Mac-style new line char.
(from the OP's comment under this answer):
Then why to give '\r\n'???
When a programmer writes a program, the programmer can make the program do whatever the programmer wants the program to do. When Windows programmers made Windows and Notepad they decided to make the program do nothing if it got a \r, nothing if it got a \n, and to do a new line if it got a \r\n together. It's that simple. The program is doing exactly what the programmers told it to do, because they decided that's how they wanted the program to work. So, if you want a new line in the older (pre-2018) version of Notepad in Windows, you must do what the programmers require you to do to get it. \r\n is it.
This goes back to the days of teletypewriters (read the "History" and "Representation" sections here), and this page about "teleprinters" / "teletypewriters" / "teletype or TTY machines" too:
A typewriter or electromechanical printer can print characters on paper, and execute operations such as move the carriage back to the left margin of the same line (carriage return), advance to the same column of the next line (line feed), and so on.
(source; emphasis added)
The mechanical carriage return button on a teletypewriter (\r now on a computer) meant: "return the carriage (print head) to the beginning of the line" (meaning: the far left side of the page), and the line feed mechanical mechanism on a teletypewriter (\n now on a computer) meant: "roll the paper up one line so we can now type onto the next line." Without the mechanical line feed (\n) action, the carriage return (\r) alone would move the mechanical print head to the far left of the page and cause you to type right back on top of the words you already typed! And without the carriage return mechanical action (\r on a computer), the line feed mechanical action (\n) alone would cause you to just type in the last column at the far right on each new line on the page, never able to return the print head to the left side of the page again! On an electro-mechanical teletypewriter, they both had to be used: the carriage return would bring the print head back to the left side of the page, and the line feed action would move the print head down to the next line. So, presumably, Windows programmers felt it was logical to keep that tradition alive, and they decided to require both a \r\n together to create a new line on a computer, since that's how it had to be done traditionally on an electro-mechanical teletypewriter.
Read below for details.
Details (the longer answer):
I have some ideas of what's going on, but let's take a look. I believe we have two questions to answer:
Is the \r actually being stored into the file?
Is Notepad actually showing the \r, and if not, why not?
So, for #1. Let's test it on Linux Ubuntu 20.04 (Focal Fossa):
This program:
#!/usr/bin/python3
import csv
data = [['fruit','quantity'], ['apple',5], ['banana',7],['mango',8]]
with open('d:\lineter.csv','w') as l:
w = csv.writer(l, delimiter='|', lineterminator='\r')
w.writerows(data)
produces this file: d:\lineter.csv. If I open it in the Sublime Text 3 text editor I see:
fruit|quantity
apple|5
banana|7
mango|8
So far so good. Let's look at the characters with hexdump at the command line:
hexdump -c shows the \r characters, sure enough!
$ hexdump -c d\:\\lineter.csv
0000000 f r u i t | q u a n t i t y \r a
0000010 p p l e | 5 \r b a n a n a | 7 \r
0000020 m a n g o | 8 \r
0000028
You can also use hexdump -C to show the characters in hexadecimal instead, and again, I see the \r in the file as a hex 0d char, which is correct.
Ok, so I boot up Windows 10 Professional in my VirtualBox virtual machine in Linux, and open the same file in Notepad, and....it works too! See screenshot:
But, notice the part I circled which says "Macintosh (CR)". I'm running the latest version of Windows 10 Professional. I'm betting you're using an old version of Notepad which doesn't have this fix, and yours won't say that here. This is because for 33 years Notepad didn't handle Carriage Return, or \r, as a valid line-ending, so it wouldn't display it as such. See here: Windows Notepad fixed after 33 years: Now it finally handles Unix, Mac OS line endings.
Due to historical differences dating back to teletypewriters and Morse code (read the "History" and "Representation" sections here), different systems decided to make their text editors treat line endings in different ways. From the article just above (emphasis added):
Notepad previously recognized only the Windows End of Line (EOL) characters, specifically Carriage Return (CR, \r, 0x0d) and Line Feed (LF, \n, 0x0a) together.
For old-school Mac OS, the EOL character is just Carriage Return (CR, \r, 0x0d) and for Linux/Unix it's just Line Feed (LF, \n, 0x0a). Modern macOS, since Mac OS X, follows the Unix convention.
So, what we have here is the following displayed as a newline in a text editor:
Old-school Mac: CR (\r) only
Windows Notepad up until ~2018: CR & LF together (\r\n)
Linux: LF (\n) only
Modern Mac: LF (\n) only
Modern Windows Notepad (year ~2018 and later): any of the scenarios above.
So, for Windows, just stick to always using \r\n for a newline, and for Mac or Linux, just stick to always using \n for a newline, unless you're trying to guarantee old-school (i.e., pre-2019 :)) Windows compatibility of your files, in which case you should use \r\n for newlines as well.
Note, for Sublime Text 3, I just searched the preferences in Preferences → Settings and found this setting:
// Determines what character(s) are used to terminate each line in new files.
// Valid values are 'system' (whatever the OS uses), 'windows' (CRLF) and
// 'unix' (LF only).
"default_line_ending": "system",
So, to use the convention for whatever OS you're running Sublime Text on, the default is "system". To force 'windows' (CRLF) line endings when editing and saving files in Sublime Text, however, use this:
"default_line_ending": "windows",
And to force Unix (Mac and Linux) LF-only line ending settings, use this:
"default_line_ending": "unix",
In the Notepad editor, I can find no such settings to configure. It is a simple editor, catering for 33 years to Windows line endings only.
Additional Reading:
https://en.wikipedia.org/wiki/Teleprinter
https://en.wikipedia.org/wiki/Newline#History
Is a new line = \n OR \r\n?
Why does Windows use CR LF?
[I still need to read & study] Unix & Linux: Why does Linux use LF as the newline character?
[I still need to read & study] Retrocomputing: Why is Windows using CR+LF and Unix just LF when Unix is the older system?
I have read all online questions on this problem and none of them seem to be working for me. I want to write a code in VBA such that when a button is pressed, my code in Python automatically starts running.
I am getting a file not found error when I run the code but I have checked the path and I know it is correct.
The code I am trying is:
Sub MyMacro()
Shell("C:/Users/RGilsburg/New folder/pythonw.exe" & "F:/Asset/Global/Port/untitled1.py")
End Sub
Can anyone tell me where the error is?
The shell command should work, however, you have some issues with the command to be executed:
You need to put a blank between the Python command and the python file.
Use the backslash, not the slash if you are on windows
If a file contains a blank, you have to put it in Double quotes ". When you want to have a quote character in a string in VBA, you have to double it.
Basically, the parameter to Shell should be the same as you would enter it on a command prompt. To check this, write the command into a string variable and write this to the immediate window (Ctrl+G). Copy it from there and paste it into a CMD-window.
Try
Dim python as string, script as string, cmd As String
python = """C:\Users\RGilsburg\New folder\pythonw.exe"""
script = "F:\Asset\Global\Port\untitled1.py"
cmd = python & " " & script
Debug.print cmd
Shell cmd
this may be a bit ignorant of me since i know nothing of python and little of vba but did you add python as a reference in the vba editor.
if not
go to the tools dropdown in the vba editor select references and see if you can find python.
I am using Vim (8.0) and tmux (2.3) together in the following way: In a tmux session I have a window split to 2 panes, one pane has some text file open in Vim, the other pane has some program to which I want to send lines of text. A typical use case is sending lines from a Python script to IPython session running in the other pane.
I am doing this by a Vim script which uses python, code snippet example (assuming the target tmux pane is 0):
py import vim
python << endpython
cmd = "print 1+2"
vim_cmd = "silent !tmux send-keys -t 0 -l \"" + cmd + "\"" # -l for literal
vim.command(vim_cmd)
endpython
This works well, except for when cmd has some characters which has to be escaped, like %, #, $, etc. The cmd variable is read from the current line in the text file opened in Vim, so I can do something like cmd = cmd.replace('%', '\%') etc., but this has 2 disadvantages: first, I don't know all the vim characters which have to be escaped, so it has been trial and error up until now, and second, the characters " is not escaped properly - that is in the string Vim gets, the " just disappears, even if I do cmd = cmd.replace('"', '\"').
So, is there a general way to tell Vim to not interpret anything, just get a raw string and send it as is? If not, why is the " not escaped properly?
Vimscript
You're looking for the shellescape() function. If you use the :! Vim command, the {special} argument needs to be 1.
silent execute '!tmux send-keys -t 0 -l ' . shellescape(cmd, 1)
But as you're not interested in (displaying) the shell output, and do not need to interact with the launched script, I would switch from :! to the lower-level system() command.
call system('tmux send-keys -t 0 -l ' . shellescape(cmd))
Python
The use of Python (instead of pure Vimscript) doesn't have any benefits (at least in the small snippet in your question). Instead, if you embed the Python cmd variable in a Vimscript expression, now you also need a Python function to escape the value as a Vimscript string (something like '%s'" % str(cmd).replace("'", "''"))). Alternatively, you could maintain the value in a Vim variable, and access it from Python via vim.vars.
When I create the file test.py (see code below) in an editor on Windows (I tried Netbeans, PyCharm and Notepad++) and upload it to the server (Ubuntu) I receive this error:
End of script output before headers: test.py
But when I create the file directly on the server using vi command line editor the page is displayed without any error. Any idea how to fix this issue ?
Here's the code for test.py
#!/usr/bin/python
# send content type
print("Content-Type: text/html\n\n")
print("Good")
I think that's because of windows carriage return characters.
These are two characters:
\r is carriage return;
\n is line feed.
Two characters combined represent a new line on Windows. Whereas on Linux, \n represents new line.
Notepad++ has an option to specify which format you want to use:
Go to Settings -- > Preferences and the choose linux:
I have a python file (/home/test.py) that has a mixture of spaces and tabs in it.
Is there a programmatic way (note: programmatic, NOT using an editor) to convert this file to use only tabs? (meaning, replace any existing 4-spaces occurrences with a single tab)?
Would be grateful for either a python code sample or a linux command to do the above. Thanks.
Sounds like a task for sed:
sed -e 's/ /\t/g' test.py > test.new
[Put a real tab instead of \t]
However...
Use 4 spaces per indentation level.
--PEP 8 -- Style Guide for Python Code
you can try iterating the file and doing replacing eg
import fileinput
for line in fileinput.FileInput("file",inplace=1):
print line.replace(" ","\t")
or you can try a *nix tool like sed/awk
$ awk '{gsub(/ /,"\t")}1' file > temp && mv temp file
$ ruby -i.bak -ne '$_.gsub!(/ /,"\t")' file