What's a standard way to do a no-op in python?
Question:
I often find myself writing if / elif / else constructs in python, and I want to include options which can occur, but for which the corresponding action is to do nothing. I realise I could just exclude those if statements, but for readability I find it helps to include them all, so that if you are looking through the code you can see what happens as a result of each option. How do I code the no-op? Currently, I’m doing it like this:
no_op = 0
if x == 0:
y = 2 * a
elif x == 1:
z = 3 * b
elif x == 3:
no_op
(The code is actually quite a bit longer than that, and more complicated. This is just to illustrate the structure).
I don’t like using a variable as a no-op, but it’s the neatest way I could think of. Is there a better way?
Answers:
Use pass for no-op:
if x == 0:
pass
else:
print "x not equal 0"
And here’s another example:
def f():
pass
Or:
class c:
pass
How about pass?
If you need a function that behaves as a nop, try
nop = lambda *a, **k: None
nop()
Sometimes I do stuff like this when I’m making dependencies optional:
try:
import foo
bar=foo.bar
baz=foo.baz
except:
bar=nop
baz=nop
# Doesn't break when foo is missing:
bar()
baz()
a simple practice on my desk just uses a line like this:
dummy = 0
the normal coder (even those which are coming from other common programming languages) will instantly understand it.
You can print an empty string and no line feed to the standard output. This can be handy if a linter prohibits you from using a pass where it is unnecessary, but you need a line for a comment:
print('', end='') # This does next to nothing
Using this empty print has very little side effects, besides wasted CPU cycles:
$ echo "print('', end='') # This does next to nothing" > main.py
$ python3 main.py
$
Note that using pass here would have been syntactically correct, but linters might complain:
$ echo "pass # This does next to nothing" > main.py
$ python3 main.py
$
As ‘return’ without args is apparently a no-op, under some code, it junked me out in analysis of some obfuscated ‘virus’ in Python for some time.
... (builtins.ellipsis) was not mentioned as a viable alternative to pass in an expression context.
def f(condition: bool) -> None:
if condition:
print("hello ", end="")
else:
pass # noop
print("world") if condition else ...
f(False) # ''
f(True) # 'hello world'
I often find myself writing if / elif / else constructs in python, and I want to include options which can occur, but for which the corresponding action is to do nothing. I realise I could just exclude those if statements, but for readability I find it helps to include them all, so that if you are looking through the code you can see what happens as a result of each option. How do I code the no-op? Currently, I’m doing it like this:
no_op = 0
if x == 0:
y = 2 * a
elif x == 1:
z = 3 * b
elif x == 3:
no_op
(The code is actually quite a bit longer than that, and more complicated. This is just to illustrate the structure).
I don’t like using a variable as a no-op, but it’s the neatest way I could think of. Is there a better way?
Use pass for no-op:
if x == 0:
pass
else:
print "x not equal 0"
And here’s another example:
def f():
pass
Or:
class c:
pass
How about pass?
If you need a function that behaves as a nop, try
nop = lambda *a, **k: None
nop()
Sometimes I do stuff like this when I’m making dependencies optional:
try:
import foo
bar=foo.bar
baz=foo.baz
except:
bar=nop
baz=nop
# Doesn't break when foo is missing:
bar()
baz()
a simple practice on my desk just uses a line like this:
dummy = 0
the normal coder (even those which are coming from other common programming languages) will instantly understand it.
You can print an empty string and no line feed to the standard output. This can be handy if a linter prohibits you from using a pass where it is unnecessary, but you need a line for a comment:
print('', end='') # This does next to nothing
Using this empty print has very little side effects, besides wasted CPU cycles:
$ echo "print('', end='') # This does next to nothing" > main.py
$ python3 main.py
$
Note that using pass here would have been syntactically correct, but linters might complain:
$ echo "pass # This does next to nothing" > main.py
$ python3 main.py
$
As ‘return’ without args is apparently a no-op, under some code, it junked me out in analysis of some obfuscated ‘virus’ in Python for some time.
... (builtins.ellipsis) was not mentioned as a viable alternative to pass in an expression context.
def f(condition: bool) -> None:
if condition:
print("hello ", end="")
else:
pass # noop
print("world") if condition else ...
f(False) # ''
f(True) # 'hello world'