Question

According to Python documentation, both dir() (without args) and locals() evaluates to the list of variables in something called local scope. First one returns list of names, second returns a dictionary of name-value pairs. Is it the only difference? Is this always valid?

assert dir() == sorted( locals().keys() )

Answer 1

The output of dir() when called without arguments is almost same as locals(), but dir() returns a list of strings and locals() returns a dictionary and you can update that dictionary to add new variables.

dir(...)
    dir([object]) -> list of strings

    If called without an argument, return the names in the current scope.


locals(...)
    locals() -> dictionary

    Update and return a dictionary containing the current scope's local variables.

---

Type:

>>> type(locals())
<type 'dict'>
>>> type(dir())
<type 'list'>

---

Update or add new variables using locals():

In [2]: locals()['a']=2

In [3]: a
Out[3]: 2

using dir(), however, this doesn’t work:

In [7]: dir()[-2]
Out[7]: 'a'

In [8]: dir()[-2]=10

In [9]: dir()[-2]
Out[9]: 'a'

In [10]: a
Out[10]: 2