I want to create variables dynamically in Python. Does anyone have any creative means of doing this?
Answers:
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Method 1
Unless there is an overwhelming need to create a mess of variable names, I would just use a dictionary, where you can dynamically create the key names and associate a value to each.
a = {}
k = 0
while k < 10:
# dynamically create key
key = ...
# calculate value
value = ...
a[key] = value
k += 1
There are also some interesting data structures in the collections module that might be applicable.
Method 2
globals() returns a dictionary of the module’s variables. You can create a new variable by creating a key on that dictionary:
# By default, a module has some hidden variables defined
print({k: v for k, v in globals().items() if not k.startswith("__")})
for i in range(1, 11):
globals()[f"my_variable_{i}"] = i
print()
print(my_variable_1)
print(my_variable_2)
# and so on
print()
print({k: v for k, v in globals().items() if not k.startswith("__")})
Result:
{}
1
2
{'i': 10, 'my_variable_1': 1, 'my_variable_2': 2, 'my_variable_3': 3, 'my_variable_4': 4, 'my_variable_5': 5, 'my_variable_6': 6, 'my_variable_7': 7, 'my_variable_8': 8, 'my_variable_9': 9, 'my_variable_10': 10}
Method 3
Use the exec() method to run arbitrary code. For example, say you have a dictionary and you want to turn each key into a variable with its original dictionary value, you can do the following:
>>> c = {"one": 1, "two": 2}
>>> for k, v in c.items():
... exec(f"{k} = {v}")
...
>>> one
1
>>> two
2
Method 4
Stuffing things into the global and/or local namespaces is not a good idea. Using a dict is so some-other-language-ish … d['constant-key'] = value just looks awkward. Python is OO. In the words of a master: “””Namespaces are one honking great idea — let’s do more of those!”””
Like this:
>>> class Record(object):
... pass
...
>>> r = Record()
>>> r.foo = 'oof'
>>> setattr(r, 'bar', 'rab')
>>> r.foo
'oof'
>>> r.bar
'rab'
>>> names = 'id description price'.split()
>>> values = [666, 'duct tape', 3.45]
>>> s = Record()
>>> for name, value in zip(names, values):
... setattr(s, name, value)
...
>>> s.__dict__ # If you are suffering from dict withdrawal symptoms
{'price': 3.45, 'id': 666, 'description': 'duct tape'}
>>>
Method 5
vars()['meta_anio_2012'] = 'translate'
Method 6
Keyword parameters allow you to pass variables from one function to another. In this way you can use the key of a dictionary as a variable name (which can be populated in your while loop). The dictionary name just needs to be preceded by ** when it is called.
# create a dictionary
>>> kwargs = {}
# add a key of name and assign it a value, later we'll use this key as a variable
>>> kwargs['name'] = 'python'
# an example function to use the variable
>>> def print_name(name):
... print name
# call the example function
>>> print_name(**kwargs)
python
Without **, kwargs is just a dictionary:
>>> print_name(kwargs)
{'name': 'python'}
Method 7
NOTE: This should be considered a discussion rather than an actual answer.
An approximate approach is to operate __main__ in the module you want to create variables. For example there’s a b.py:
#!/usr/bin/env python
# coding: utf-8
def set_vars():
import __main__
print '__main__', __main__
__main__.B = 1
try:
print B
except NameError as e:
print e
set_vars()
print 'B: %s' % B
Running it would output
$ python b.py name 'B' is not defined __main__ <module '__main__' from 'b.py'> B: 1
But this approach only works in a single module script, because the __main__ it import will always represent the module of the entry script being executed by python, this means that if b.py is involved by other code, the B variable will be created in the scope of the entry script instead of in b.py itself. Assume there is a script a.py:
#!/usr/bin/env python
# coding: utf-8
try:
import b
except NameError as e:
print e
print 'in a.py: B', B
Running it would output
$ python a.py name 'B' is not defined __main__ <module '__main__' from 'a.py'> name 'B' is not defined in a.py: B 1
Note that the __main__ is changed to 'a.py'.
Method 8
For free-dom:
import random
alphabet = tuple('abcdefghijklmnopqrstuvwxyz')
globkeys = globals().keys()
globkeys.append('globkeys') # because name 'globkeys' is now also in globals()
print 'globkeys==',globkeys
print
print "globals().keys()==",globals().keys()
for i in xrange(8):
globals()[''.join(random.sample(alphabet,random.randint(3,26)))] = random.choice(alphabet)
del i
newnames = [ x for x in globals().keys() if x not in globkeys ]
print
print 'newnames==',newnames
print
print "globals().keys()==",globals().keys()
print
print 'n'.join(repr((u,globals()[u])) for u in newnames)
Result
globkeys== ['__builtins__', 'alphabet', 'random', '__package__', '__name__', '__doc__', 'globkeys']
globals().keys()== ['__builtins__', 'alphabet', 'random', '__package__', '__name__', 'globkeys', '__doc__']
newnames== ['fztkebyrdwcigsmulnoaph', 'umkfcvztleoij', 'kbutmzfgpcdqanrivwsxly', 'lxzmaysuornvdpjqfetbchgik', 'wznptbyermclfdghqxjvki', 'lwg', 'vsolxgkz', 'yobtlkqh']
globals().keys()== ['fztkebyrdwcigsmulnoaph', 'umkfcvztleoij', 'newnames', 'kbutmzfgpcdqanrivwsxly', '__builtins__', 'alphabet', 'random', 'lxzmaysuornvdpjqfetbchgik', '__package__', 'wznptbyermclfdghqxjvki', 'lwg', 'x', 'vsolxgkz', '__name__', 'globkeys', '__doc__', 'yobtlkqh']
('fztkebyrdwcigsmulnoaph', 't')
('umkfcvztleoij', 'p')
('kbutmzfgpcdqanrivwsxly', 'a')
('lxzmaysuornvdpjqfetbchgik', 'n')
('wznptbyermclfdghqxjvki', 't')
('lwg', 'j')
('vsolxgkz', 'w')
('yobtlkqh', 'c')
Another way:
import random
pool_of_names = []
for i in xrange(1000):
v = 'LXM'+str(random.randrange(10,100000))
if v not in globals():
pool_of_names.append(v)
alphabet = 'abcdefghijklmnopqrstuvwxyz'
print 'globals().keys()==',globals().keys()
print
for j in xrange(8):
globals()[pool_of_names[j]] = random.choice(alphabet)
newnames = pool_of_names[0:j+1]
print
print 'globals().keys()==',globals().keys()
print
print 'n'.join(repr((u,globals()[u])) for u in newnames)
result:
globals().keys()== ['__builtins__', 'alphabet', 'random', '__package__', 'i', 'v', '__name__', '__doc__', 'pool_of_names']
globals().keys()== ['LXM7646', 'random', 'newnames', 'LXM95826', 'pool_of_names', 'LXM66380', 'alphabet', 'LXM84070', '__package__', 'LXM8644', '__doc__', 'LXM33579', '__builtins__', '__name__', 'LXM58418', 'i', 'j', 'LXM24703', 'v']
('LXM66380', 'v')
('LXM7646', 'a')
('LXM8644', 'm')
('LXM24703', 'r')
('LXM58418', 'g')
('LXM84070', 'c')
('LXM95826', 'e')
('LXM33579', 'j')
All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0