Python equivalent for MySQL's IFNULL

Is there a function in Python that checks i开发者_开发知识库f the returned value is None and if it is, allows you to set it to another value like the IFNULL function in MySQL?

---

If you want to convert all "falsy" values (i.e. None, 0, "", [], False, etc.) to a specific value and let everything else through untouched, you can use or. For example:

print (x or default_value)

will print the value of x if it's truthy, and the value of default_value if x is falsy.

I mention this because IFNULL is often used this way to clean up nulls in boolean and numerical columns in a database and so might be what you or others were after. Obviously, if you want to treat None differently to 0, False, etc. this won't work.

---

Not really, since you can't rebind arguments.

if foo is None:
  foo = 42

or

def ifnull(var, val):
  if var is None:
    return val
  return var

foo = ifnull(foo, 42)

---

Like this:

x = SOME_VALUE if x is None else x

---

nvl(v1,v2) will return v1 if not null otherwise it returns v2.

nvl = lambda a,b: a or b

---

From MySQL:

nvl(foo, bar) [or even nvl2(foo, baz, bar) in Oracle]

---

Using Python ternary operator (see detailed explaination here) within a lambda function as follows:

nvl = lambda foo, bar: bar if foo is None else foo

nvl2 = lambda foo, baz, bar: bar if foo is None else baz


foo = nvl(foo, 42) # returns 42 if foo is null

foo = nvl2(foo, 7, 42) # returns 42 if foo is null or 7 is foo is not null

---

We made this one:

def d_nvl(d,key,default_val):
    try:
        return d[key]
    except Exception:
        return default_val

and it is used this way: my_val = d_nvl(my_dict,'my_key','default_val')

---

I'm using SQL Oracle, it has NVL() function which replaces null. For example, NVL(null,1) returns 1 and NVL(3,1) returns 3. Simple python equivalent for that function:

import numpy as np

nvl = lambda a,b: b if np.isnan(a) else a

nvl(3,1)
>>> 3
nvl(np.nan,1)
>>> 1

---

Since this question is now over 2 years old I guess this is more for future references :)

What I like to do is max('', mightBeNoneVar) or max(0, mightBeNoneVar) (depending on the context).

More elaborate example:
print max('', col1).ljust(width1) + ' ==> '+ max('', col2).ljust(width2)