Org Mode Babel - Interactive code block evaluation in Python

Question

Similarly to this question I would like to evaluate (in org mode) Python source code blocks containing "input" instructions but I can't find a way to have an interactive evaluation (with user input) during evaluation or to give it some input known in advance (stored in a file for instance).

My constraint is to use explicitly the input instruction since all this should be included in a textbook for students.

Example of code :

#+BEGIN_SRC python :results output 
a= input("Value") 
print(a)
#+END_SRC

Is it possible to have such an interactive evaluation or to simulate it (by giving to the source code a fake input) ?

Answer 1

Here is an alternative approach that uses a non-exported, tangled file to replace the input function.

#+BEGIN_SRC python :session :exports none :tangle example1.py
def input(x): 
    if x == 'Value of a':
        return 3
    elif x == 'Value of b':
        return 4 

#+END_SRC 

#+RESULTS: 

Tip: Press C-cC-vt or use the M-xorg-babel-tangle command to create, i.e. tangle, the example1.py file.

---

#+BEGIN_SRC python :results output :preamble from example1 import *
a = input('Value of a')
b = input('Value of b')
print(a + b) 
#+END_SRC 

#+RESULTS:
: 7

Note: The example1.py file that was created from the previous python SRC block will be imported into the current block using the builtin :preamble header and the value from example1 import *.

Answer 2

Evaluate python code blocks using literate programming in org-mode.

Use :var header to assign variables and test your code.

Note: If desired use elisp (read-string "Prompt: ") and (read-number "Prompt: ") to prompt for user input inside emacs.

---

Example 1 - print(a)

• Assign hello world to a.

  ---

  #+name: ex1-code  
  #+header: :var a="hello world"  
  #+begin_src python :results verbatim replace output :exports results  
    print(a)  
  #+end_src
  
  #+begin_src python :eval never :exports code :noweb yes   
    a = input('Value of a')  
    <<ex1-code>>  
  #+end_src  
  
  #+results: ex1-code
  : hello world
  

  ---

Example 2 - print(a + b)

• Assign 1 to a.

• Assign 2 to b.

  ---

  #+name: ex2-code
  #+header: :var a=1 
  #+header: :var b=2 
  #+begin_src python :results replace output  :exports results 
    print(a + b)
  #+end_src
  
  #+begin_src python :eval never :exports code :noweb yes 
    a = input('Value of a')
    b = input('Value of b')
    <<ex2-code>>
  #+end_src  
  
  #+results: ex2-code
  : 3
  

  ---

Example 3 - print(a,b,c)

• When prompted for Value of a enter Thanks
• When prompted for Value of b enter 4.

• When prompted for Value of c enter your question.

  ---

  #+NAME: ex3-code
  #+header: :var a=(read-string "Value of a ") 
  #+header: :var b=(read-number "Value of b ") 
  #+header: :var c=(read-string "Value of c ") 
  #+begin_src python :results replace output   :exports results 
    print a,b,c
  #+end_src  
  
  #+begin_src python :eval never :exports code :noweb yes 
    a = input('Value of a')
    b = input('Value of b')
    c = input('Value of c')
    <<ex3-code>>
  #+end_src  
  
  #+results: ex3-code
  : Thanks 4 your question
  

  ---

When you export your org file, the output should look similar to the example below

---

Example 1 - print(a)

• Assign hello world to a.

  a = input('Value of a')
  print(a)
  
  hello world
  

Example 2 - print(a + b)

• Assign 1 to a.

• Assign 2 to b.

  a = input('Value of a')
  b = input('Value of b')
  print(a + b)
  
  3
  

Example 3 - print(a,b,c)

• When prompted for Value of a enter Thanks
• When prompted for Value of b enter 4.

• When prompted for Value of c enter your question.

  a = input('Value of a')
  b = input('Value of b')
  c = input('Value of c')
  print a,b,c
  
  Thanks 4 your question
  

---

---

This code was tested with
GNU Emacs 24.5.1 (x86_64-unknown-cygwin, GTK+ Version 3.14.13)
Org-Mode Version: 8.3.2
and github.

Answer 3

I don't think it is possible to get truly interactive Python input with org-babel.

You could use a preamble to redefine the input function so it returns what you want to simulate the use of input, e.g. here we make it look like the user typed in "3".

#+BEGIN_SRC python :results output :preamble def input(x): return 3
a = input("value ")
print(a)
#+END_SRC

#+RESULTS:
: 3

Depending on what students see that is exported, they might not see that you have done this.

Answer 4

As a complement of John Kitchin's solution, I propose to use a generator to provide the successive values that will "feed" the input(...) functions and to return a strobject systematically.

#+BEGIN_SRC python :session :exports none :tangle example2.py :results none
def generate(lst):
    for element in lst:
        yield str(element)

generator =  generate(["Thanks",4,"your help"])

def input(x):
     return generator.__next__()
#+END_SRC 


#+BEGIN_SRC python :results output :preamble from example2 import * :exports both
a = input('Value of a')
b = input('Value of b')
c = input('Value of c')
print(a,b,c)
#+END_SRC