有没有办法使用变量内的字符串调用 Python 中的方法？

Question

I'm new to coding so please forgive me if this question have already been answered elsewhere, but I tried looking for awhile and couldn't find an answer.

To clarify the issue I am trying to solve, I'll illustrate it with the code below:

#Sample problem
ABCD = []
KEY = "ABCD"
data = 123
[str(KEY)].append(data)

print(f"{ABCD}")

Here I am attempting to call the append method for the list ABCD but with the variable KEY which contains the string "ABCD" This code doesn't work but illustrates my question. I am wondering if it is possible to call the method such as the one I have above using a variable instead of hard coding it like:

if KEY == "ABCD":
    ABCD.append(data)

print(f"{ABCD}")

Thank you!!

Answer 1

I think I shall share my method not using eval . It accesses all the local variables currently in the script. The program uses this to it's advantage allowing it to locate whether a variable exists or not. Another thing used in this program are dictionaries which help us store our information neatly. Though it might be a tad bit overcomplicated Testcase 1 # ABCD does exist

ABCD = []
KEY = "ABDC"
data = 123
import sys, pprint
sys.displayhook = pprint.pprint
variables = locals()
#check if KEY can be found in locals
if variables.get(KEY) != None:
    #create a dict ,KEY = key, "[]" is value
    #{'ABCD': []}
    varDict = {KEY:variables.get(KEY)}
    #append data
    varDict[KEY].append(data)
    print(varDict)
#KEY is not variable in locals
else:
    print('could not find')

expected output

{'ABCD': [123]}

Testcase 2 #ABCD is not existant, instead ABDC .

ABCD = []
KEY = "ABDC"
data = 123
import sys, pprint
sys.displayhook = pprint.pprint
variables = locals()
#check if KEY can be found in locals
if variables.get(KEY) != None:
    #create a dict ,KEY = key, "[]" is value
    #{'ABCD': []}
    varDict = {KEY:variables.get(KEY)}
    #append data
    varDict[KEY].append(data)
    print(varDict)
#KEY is not variable in locals
else:
    print('could not find')

expected output

could not find

Let me know if a test case does not work.

Answer 2

You can pass eval an f string to do that, but furas' method is much safer/better.

ABCD = []
KEY = "ABCD"
data = 123
eval(f'{KEY}.append(data)')
print(ABCD)

More on the dangers of eval here

In addition, there are a number of methods for storing and referencing objects without having to put them into a key-value pair relationship (in dict) but furas' method is the most direct and useful for most cases.