我想在Python中动态创建变量。有人有什么创造性的方法吗?
当前回答
关键字参数允许将变量从一个函数传递到另一个函数。通过这种方式,您可以使用字典的键作为变量名(可以在while循环中填充)。当它被调用时,字典名只需要在前面加上**。
# 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
没有**,kwargs只是一个字典:
>>> print_name(kwargs)
{'name': 'python'}
其他回答
注意:这应该被认为是一个讨论,而不是一个实际的答案。
一个近似的方法是在你想要创建变量的模块中操作__main__。例如,有一个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
运行它会输出
$ python b.py
name 'B' is not defined
__main__ <module '__main__' from 'b.py'>
B: 1
但是这种方法只适用于单个模块脚本,因为__main__ it导入将始终表示python正在执行的入口脚本的模块,这意味着如果B .py被其他代码涉及,B变量将在入口脚本的范围内创建,而不是在B .py本身中。假设有一个脚本a.py:
#!/usr/bin/env python
# coding: utf-8
try:
import b
except NameError as e:
print e
print 'in a.py: B', B
运行它会输出
$ python a.py
name 'B' is not defined
__main__ <module '__main__' from 'a.py'>
name 'B' is not defined
in a.py: B 1
注意,__main__被更改为'a.py'。
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)
结果
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')
另一种方法:
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)
结果:
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')
vars()['meta_anio_2012'] = 'translate'
关键字参数允许将变量从一个函数传递到另一个函数。通过这种方式,您可以使用字典的键作为变量名(可以在while循环中填充)。当它被调用时,字典名只需要在前面加上**。
# 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
没有**,kwargs只是一个字典:
>>> print_name(kwargs)
{'name': 'python'}
除非非常需要创建一堆变量名,否则我会使用字典,在字典中您可以动态地创建键名并将值关联到每个键名。
a = {}
k = 0
while k < 10:
# dynamically create key
key = ...
# calculate value
value = ...
a[key] = value
k += 1
collections模块中还有一些有趣的数据结构可能适用。