0

I was doing some bash scripting and adding some python for float calculations like divide, deductions

When I am executing this, all part is running fine but for some python part it is showing me an error, however, in the latter part, it is showing me correct calculations.

File "<string>", line 1
    print 0.05-
              ^
SyntaxError: invalid syntax
  File "<string>", line 1
    print /2
          ^
SyntaxError: invalid syntax

My script is like the following:

tx_fee=0.0001;
panda_txfee=$(python -c "print $check_t_balance-$tx_fee");
panda=$(python -c "print $panda_txfee/2");

What I am doing wrong?

8
  • 1
    Do those variables have actual values? An unassigned variable expands to the empty string, which this looks like. (I assume you have $check_t_balance set somewhere?) Feb 7 '19 at 12:31
  • yes, at the begining I declared all the variables with either int or float values
    – Rakib Fiha
    Feb 7 '19 at 12:32
  • 1
    If I set check_t_balance=1 and run your code, I get $panda as 0.49995. I think you're just not setting the check_t_balance variable. Also, Python is a bit heavy weight just for doing floating point arithmetics in the shell. Either use something less heavy, such as bc, or do it all in one single Python program.
    – Kusalananda
    Feb 7 '19 at 12:35
  • 2
    To answer questions about possible problems with your variables we would have to see how you set the variables, what you do with functions etc. You should try to create a minimal script that reproduces the problem.
    – Bodo
    Feb 7 '19 at 12:47
  • 1
    for your division problem see stackoverflow.com/questions/1267869/…
    – Bodo
    Feb 7 '19 at 13:08
2

That works:

> tx_fee=0.0001;
> panda_txfee=$(python -c "print $check_t_balance-$tx_fee");
> panda=$(python -c "print $panda_txfee/2");
>
> echo $panda
-5e-05

Your errors show that variable panda_txfree is empty:

  File "<string>", line 1
    print /2
          ^
SyntaxError: invalid syntax

and it is empty because of tx_fee is empty:

File "<string>", line 1
    print 0.05-
              ^
SyntaxError: invalid syntax

provide more details of your environment.

Also note, I'm using Python 2.7 (and Bash), for Python 3 you will need embrace print arguments in round parenthesis, like this: print($panda_txfee/2), because in Python 3 print is a function, not special keyword for printing out.

4
  • Tonight I am offline from that unix now, I will post it tomorrow.
    – Rakib Fiha
    Feb 7 '19 at 13:49
  • I am using Python 2.7 as well. I think, I found the mistake, I did a silly spelling mistake, Everywhere I used the variable tx_fee but only in one place I wrote tx_fees, I will test it tomorrow. I hope this was the main and only reason of this error. I was thinking, I have many floats so is it better to wrap it within float function like this? or its just useless? amt=$(python -c "print(float($amt_aft_txfee/2))");
    – Rakib Fiha
    Feb 7 '19 at 15:50
  • 1
    @RakibFiha, you can omit float() if value in your amt_aft_txfee variable goes with point, e.g. 2.5 or 2.0 also note, that in Python usually used Decimal (from module decimal) wrapper for precise calculations
    – rook
    Feb 7 '19 at 16:02
  • 1
    @RakibFiha, In python 2, you might want float(x)/2, since x/2 would round/truncate the result if x is an integer. float(x/2) doesn't help in that, the conversion happens too late there
    – ilkkachu
    Feb 7 '19 at 16:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.