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6

Take this example:

>>> 5+10

15

>>> a = 5 + 10

>>> a

15

My question is how and why python does this without an explicit print statement?

If I do the same thing in an IPython cell, only the last such value is actually printed on stdout in this way:

In[1]: 5+10

       1



Out[1]: 1

Why does this happen?

python printing stdout

share|improve this question

asked 4 hours ago

Chayan GhoshChayan Ghosh

956

add a comment | 

6

Take this example:

>>> 5+10

15

>>> a = 5 + 10

>>> a

15

My question is how and why python does this without an explicit print statement?

If I do the same thing in an IPython cell, only the last such value is actually printed on stdout in this way:

In[1]: 5+10

       1



Out[1]: 1

Why does this happen?

python printing stdout

share|improve this question

asked 4 hours ago

Chayan GhoshChayan Ghosh

956

add a comment | 

Take this example:

>>> 5+10

15

>>> a = 5 + 10

>>> a

15

My question is how and why python does this without an explicit print statement?

If I do the same thing in an IPython cell, only the last such value is actually printed on stdout in this way:

In[1]: 5+10

       1



Out[1]: 1

Why does this happen?

python printing stdout

share|improve this question

asked 4 hours ago

Chayan GhoshChayan Ghosh

956

>>> 5+10

15

>>> a = 5 + 10

>>> a

15

In[1]: 5+10

       1



Out[1]: 1

share|improve this question

asked 4 hours ago

Chayan GhoshChayan Ghosh

956

share|improve this question

asked 4 hours ago

Chayan GhoshChayan Ghosh

956

asked 4 hours ago

Chayan GhoshChayan Ghosh

956

asked 4 hours ago

Chayan GhoshChayan Ghosh

956

2 Answers
2

active

oldest

votes

9

When Python is in "interactive" mode, it enables certain behaviors it doesn't have in non-interactive mode. For example, sys.displayhook, originally specified in PEP 217.

If value is not None, this function prints it to sys.stdout, and saves it in builtin._.

sys.displayhook is called on the result of evaluating an expression entered in an interactive Python session.

You can modify this behavior

>>> import sys

>>> def shook(expr):

...   print(f'can haz {expr}?')

...

>>> sys.displayhook = shook

>>> 123

can haz 123?

>>> False

can haz False?

>>> None

can haz None?

and also set it back to normal:

>>> sys.displayhook = sys.__displayhook__

>>> 3

3

In the default python repl, sys.displayhook is

>>> import sys;

>>> sys.displayhook

<built-in function displayhook>

but in IPython it's

In [1]: import sys



In [2]: sys.displayhook

Out[2]: <IPython.terminal.prompts.RichPromptDisplayHook at 0x7f630717fa58>

So that's why you see different behavior between python and ipython.

share|improve this answer

edited 4 hours ago

answered 4 hours ago

kojirokojiro

53.5k1387138

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  didn't know about the displayhook feature. Very helpful, thanks.
  
  – Chayan Ghosh
  4 hours ago
  

  
  
  
  

add a comment | 

1

That's how all interpreters work, they don't need any print, but one thing, without print does the repr of everything, and print doesn't, example:

>>> 'blah'

'blah'

>>> print('blah')

blah

>>> 

Look at the quotes.

Also see this:

>>> print(repr('blah'))

'blah'

>>> 

repr does the same.

share|improve this answer

edited 4 hours ago

answered 4 hours ago

U9-ForwardU9-Forward

15.7k51540

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  any comment on the IPython behavior?
  
  – Chayan Ghosh
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Let's say CPython in interactive mode works like that.
  
  – Klaus D.
  4 hours ago
  

  
  
  
  

add a comment | 

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9

When Python is in "interactive" mode, it enables certain behaviors it doesn't have in non-interactive mode. For example, sys.displayhook, originally specified in PEP 217.

If value is not None, this function prints it to sys.stdout, and saves it in builtin._.

sys.displayhook is called on the result of evaluating an expression entered in an interactive Python session.

You can modify this behavior

>>> import sys

>>> def shook(expr):

...   print(f'can haz {expr}?')

...

>>> sys.displayhook = shook

>>> 123

can haz 123?

>>> False

can haz False?

>>> None

can haz None?

and also set it back to normal:

>>> sys.displayhook = sys.__displayhook__

>>> 3

3

In the default python repl, sys.displayhook is

>>> import sys;

>>> sys.displayhook

<built-in function displayhook>

but in IPython it's

In [1]: import sys



In [2]: sys.displayhook

Out[2]: <IPython.terminal.prompts.RichPromptDisplayHook at 0x7f630717fa58>

So that's why you see different behavior between python and ipython.

share|improve this answer

edited 4 hours ago

answered 4 hours ago

kojirokojiro

53.5k1387138

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  didn't know about the displayhook feature. Very helpful, thanks.
  
  – Chayan Ghosh
  4 hours ago
  

  
  
  
  

add a comment | 

9

When Python is in "interactive" mode, it enables certain behaviors it doesn't have in non-interactive mode. For example, sys.displayhook, originally specified in PEP 217.

If value is not None, this function prints it to sys.stdout, and saves it in builtin._.

sys.displayhook is called on the result of evaluating an expression entered in an interactive Python session.

You can modify this behavior

>>> import sys

>>> def shook(expr):

...   print(f'can haz {expr}?')

...

>>> sys.displayhook = shook

>>> 123

can haz 123?

>>> False

can haz False?

>>> None

can haz None?

and also set it back to normal:

>>> sys.displayhook = sys.__displayhook__

>>> 3

3

In the default python repl, sys.displayhook is

>>> import sys;

>>> sys.displayhook

<built-in function displayhook>

but in IPython it's

In [1]: import sys



In [2]: sys.displayhook

Out[2]: <IPython.terminal.prompts.RichPromptDisplayHook at 0x7f630717fa58>

So that's why you see different behavior between python and ipython.

share|improve this answer

edited 4 hours ago

answered 4 hours ago

kojirokojiro

53.5k1387138

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  didn't know about the displayhook feature. Very helpful, thanks.
  
  – Chayan Ghosh
  4 hours ago
  

  
  
  
  

add a comment | 

When Python is in "interactive" mode, it enables certain behaviors it doesn't have in non-interactive mode. For example, sys.displayhook, originally specified in PEP 217.

If value is not None, this function prints it to sys.stdout, and saves it in builtin._.

sys.displayhook is called on the result of evaluating an expression entered in an interactive Python session.

You can modify this behavior

>>> import sys

>>> def shook(expr):

...   print(f'can haz {expr}?')

...

>>> sys.displayhook = shook

>>> 123

can haz 123?

>>> False

can haz False?

>>> None

can haz None?

and also set it back to normal:

>>> sys.displayhook = sys.__displayhook__

>>> 3

3

In the default python repl, sys.displayhook is

>>> import sys;

>>> sys.displayhook

<built-in function displayhook>

but in IPython it's

In [1]: import sys



In [2]: sys.displayhook

Out[2]: <IPython.terminal.prompts.RichPromptDisplayHook at 0x7f630717fa58>

So that's why you see different behavior between python and ipython.

share|improve this answer

edited 4 hours ago

answered 4 hours ago

kojirokojiro

53.5k1387138

>>> import sys

>>> def shook(expr):

...   print(f'can haz {expr}?')

...

>>> sys.displayhook = shook

>>> 123

can haz 123?

>>> False

can haz False?

>>> None

can haz None?

>>> sys.displayhook = sys.__displayhook__

>>> 3

3

>>> import sys;

>>> sys.displayhook

<built-in function displayhook>

In [1]: import sys



In [2]: sys.displayhook

Out[2]: <IPython.terminal.prompts.RichPromptDisplayHook at 0x7f630717fa58>

share|improve this answer

edited 4 hours ago

answered 4 hours ago

kojirokojiro

53.5k1387138

answered 4 hours ago

kojirokojiro

53.5k1387138

answered 4 hours ago

kojirokojiro

53.5k1387138

1

That's how all interpreters work, they don't need any print, but one thing, without print does the repr of everything, and print doesn't, example:

>>> 'blah'

'blah'

>>> print('blah')

blah

>>> 

Look at the quotes.

Also see this:

>>> print(repr('blah'))

'blah'

>>> 

repr does the same.

share|improve this answer

edited 4 hours ago

answered 4 hours ago

U9-ForwardU9-Forward

15.7k51540

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  any comment on the IPython behavior?
  
  – Chayan Ghosh
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Let's say CPython in interactive mode works like that.
  
  – Klaus D.
  4 hours ago
  

  
  
  
  

add a comment | 

1

That's how all interpreters work, they don't need any print, but one thing, without print does the repr of everything, and print doesn't, example:

>>> 'blah'

'blah'

>>> print('blah')

blah

>>> 

Look at the quotes.

Also see this:

>>> print(repr('blah'))

'blah'

>>> 

repr does the same.

share|improve this answer

edited 4 hours ago

answered 4 hours ago

U9-ForwardU9-Forward

15.7k51540

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  any comment on the IPython behavior?
  
  – Chayan Ghosh
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Let's say CPython in interactive mode works like that.
  
  – Klaus D.
  4 hours ago
  

  
  
  
  

add a comment | 

That's how all interpreters work, they don't need any print, but one thing, without print does the repr of everything, and print doesn't, example:

>>> 'blah'

'blah'

>>> print('blah')

blah

>>> 

Look at the quotes.

Also see this:

>>> print(repr('blah'))

'blah'

>>> 

repr does the same.

share|improve this answer

edited 4 hours ago

answered 4 hours ago

U9-ForwardU9-Forward

15.7k51540

>>> 'blah'

'blah'

>>> print('blah')

blah

>>> 

>>> print(repr('blah'))

'blah'

>>> 

share|improve this answer

edited 4 hours ago

answered 4 hours ago

U9-ForwardU9-Forward

15.7k51540

answered 4 hours ago

U9-ForwardU9-Forward

15.7k51540

answered 4 hours ago

U9-ForwardU9-Forward

15.7k51540