IPython notebook: using quotes(') and dollar($) to pass string variable as argument to python script in command-line(!) | eg: abc.py -arg1 '$var1'

Question

In using variables in the command line from a notebook cell, I saw that we can use put a $ in front of the variable, or surround the variable using {} , for example

!command {variable}

or

!command $variable

But when I was running a python script using the command line from a notebook cell, I would get errors

variable1 = '/path/to/directory'
variable2 = 7

!Script.py -arg1 $variable1 -arg2 $variable2

and

!Script.py -arg1 {variable1} -arg2 {variable2}

did not work.

After experimenting a little bit, I found that if a variable is a string, surrounding the whole arg with quotes got it to work.

variable1 = '/path/to/directory'
variable2 = 7

!Script.py -arg1 '$variable1' -arg2 $variable2

What is going on? I tried to look up this phenomena but I couldn't find anything.

If it makes a difference, I am using google colab colaboratory

Would it be too much work to tell us what the errors were? I'm too lazy test this code myself. — hpaulj, Aug 02 '19 at 18:14
A possible point of confusion is the `bash`, the shell, itself can do '$' expansions. — hpaulj, Aug 02 '19 at 18:51

score 0 · Answer 1 · answered Nov 22 '19 at 02:50

0

Have you tried?

!Script.py -arg1 $variable1\ -arg2 $variable2\

answered Nov 22 '19 at 02:50

JoeBlender

49
1

Chong Onn Keat · Answer 2 · 2021-10-04T16:10:31.073

Any input line beginning with a ! character is passed verbatim(exclude the !) to the underlying command-line interface. [source]

Passing a string variable after ! character will pass only the string content, but not the '(quotes) symbol. You need to surround the string variable with '(quotes) symbol in your line.

Using your example above, the two variables:

variable1 = '/path/to/directory'
variable2 = 7

When running this line:

!Script.py -arg1 $variable1 -arg2 $variable2         #wrong

it will translate to

> Script.py -arg1 /path/to/directory -arg2 7

the quotation mark is not passed to the command-line.

So, you need to add the quotation mark around the string variable:

!Script.py -arg1 '$variable1' -arg2 $variable2       #correct

that will translate to

> Script.py -arg1 '/path/to/directory' -arg2 7

the quotation mark is passed to the command-line. The command will work properly and your observation is correct.

IPython notebook: using quotes(') and dollar($) to pass string variable as argument to python script in command-line(!) | eg: abc.py -arg1 '$var1'

2 Answers2

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