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Getting the name of a variable as a string
(32 answers)
Closed 4 months ago.
Is it possible to get the original variable name of a variable passed to a function? E.g.
foobar = "foo"
def func(var):
print var.origname
So that:
func(foobar)
Returns:
>>foobar
EDIT:
All I was trying to do was make a function like:
def log(soup):
f = open(varname+'.html', 'w')
print >>f, soup.prettify()
f.close()
.. and have the function generate the filename from the name of the variable passed to it.
I suppose if it's not possible I'll just have to pass the variable and the variable's name as a string each time.
EDIT: To make it clear, I don't recommend using this AT ALL, it will break, it's a mess, it won't help you in any way, but it's doable for entertainment/education purposes.
You can hack around with the inspect module, I don't recommend that, but you can do it...
import inspect
def foo(a, f, b):
frame = inspect.currentframe()
frame = inspect.getouterframes(frame)[1]
string = inspect.getframeinfo(frame[0]).code_context[0].strip()
args = string[string.find('(') + 1:-1].split(',')
names = []
for i in args:
if i.find('=') != -1:
names.append(i.split('=')[1].strip())
else:
names.append(i)
print names
def main():
e = 1
c = 2
foo(e, 1000, b = c)
main()
Output:
['e', '1000', 'c']
To add to Michael Mrozek's answer, you can extract the exact parameters versus the full code by:
import re
import traceback
def func(var):
stack = traceback.extract_stack()
filename, lineno, function_name, code = stack[-2]
vars_name = re.compile(r'\((.*?)\).*$').search(code).groups()[0]
print vars_name
return
foobar = "foo"
func(foobar)
# PRINTS: foobar
Looks like Ivo beat me to inspect, but here's another implementation:
import inspect
def varName(var):
lcls = inspect.stack()[2][0].f_locals
for name in lcls:
if id(var) == id(lcls[name]):
return name
return None
def foo(x=None):
lcl='not me'
return varName(x)
def bar():
lcl = 'hi'
return foo(lcl)
bar()
# 'lcl'
Of course, it can be fooled:
def baz():
lcl = 'hi'
x='hi'
return foo(lcl)
baz()
# 'x'
Moral: don't do it.
Another way you can try if you know what the calling code will look like is to use traceback:
def func(var):
stack = traceback.extract_stack()
filename, lineno, function_name, code = stack[-2]
code will contain the line of code that was used to call func (in your example, it would be the string func(foobar)). You can parse that to pull out the argument
You can't. It's evaluated before being passed to the function. All you can do is pass it as a string.
#Ivo Wetzel's answer works in the case of function call are made in one line, like
e = 1 + 7
c = 3
foo(e, 100, b=c)
In case that function call is not in one line, like:
e = 1 + 7
c = 3
foo(e,
1000,
b = c)
below code works:
import inspect, ast
def foo(a, f, b):
frame = inspect.currentframe()
frame = inspect.getouterframes(frame)[1]
string = inspect.findsource(frame[0])[0]
nodes = ast.parse(''.join(string))
i_expr = -1
for (i, node) in enumerate(nodes.body):
if hasattr(node, 'value') and isinstance(node.value, ast.Call)
and hasattr(node.value.func, 'id') and node.value.func.id == 'foo' # Here goes name of the function:
i_expr = i
break
i_expr_next = min(i_expr + 1, len(nodes.body)-1)
lineno_start = nodes.body[i_expr].lineno
lineno_end = nodes.body[i_expr_next].lineno if i_expr_next != i_expr else len(string)
str_func_call = ''.join([i.strip() for i in string[lineno_start - 1: lineno_end]])
params = str_func_call[str_func_call.find('(') + 1:-1].split(',')
print(params)
You will get:
[u'e', u'1000', u'b = c']
But still, this might break.
You can use python-varname package
from varname import nameof
s = 'Hey!'
print (nameof(s))
Output:
s
Package below:
https://github.com/pwwang/python-varname
For posterity, here's some code I wrote for this task, in general I think there is a missing module in Python to give everyone nice and robust inspection of the caller environment. Similar to what rlang eval framework provides for R.
import re, inspect, ast
#Convoluted frame stack walk and source scrape to get what the calling statement to a function looked like.
#Specifically return the name of the variable passed as parameter found at position pos in the parameter list.
def _caller_param_name(pos):
#The parameter name to return
param = None
#Get the frame object for this function call
thisframe = inspect.currentframe()
try:
#Get the parent calling frames details
frames = inspect.getouterframes(thisframe)
#Function this function was just called from that we wish to find the calling parameter name for
function = frames[1][3]
#Get all the details of where the calling statement was
frame,filename,line_number,function_name,source,source_index = frames[2]
#Read in the source file in the parent calling frame upto where the call was made
with open(filename) as source_file:
head=[source_file.next() for x in xrange(line_number)]
source_file.close()
#Build all lines of the calling statement, this deals with when a function is called with parameters listed on each line
lines = []
#Compile a regex for matching the start of the function being called
regex = re.compile(r'\.?\s*%s\s*\(' % (function))
#Work backwards from the parent calling frame line number until we see the start of the calling statement (usually the same line!!!)
for line in reversed(head):
lines.append(line.strip())
if re.search(regex, line):
break
#Put the lines we have groked back into sourcefile order rather than reverse order
lines.reverse()
#Join all the lines that were part of the calling statement
call = "".join(lines)
#Grab the parameter list from the calling statement for the function we were called from
match = re.search('\.?\s*%s\s*\((.*)\)' % (function), call)
paramlist = match.group(1)
#If the function was called with no parameters raise an exception
if paramlist == "":
raise LookupError("Function called with no parameters.")
#Use the Python abstract syntax tree parser to create a parsed form of the function parameter list 'Name' nodes are variable names
parameter = ast.parse(paramlist).body[0].value
#If there were multiple parameters get the positional requested
if type(parameter).__name__ == 'Tuple':
#If we asked for a parameter outside of what was passed complain
if pos >= len(parameter.elts):
raise LookupError("The function call did not have a parameter at postion %s" % pos)
parameter = parameter.elts[pos]
#If there was only a single parameter and another was requested raise an exception
elif pos != 0:
raise LookupError("There was only a single calling parameter found. Parameter indices start at 0.")
#If the parameter was the name of a variable we can use it otherwise pass back None
if type(parameter).__name__ == 'Name':
param = parameter.id
finally:
#Remove the frame reference to prevent cyclic references screwing the garbage collector
del thisframe
#Return the parameter name we found
return param
If you want a Key Value Pair relationship, maybe using a Dictionary would be better?
...or if you're trying to create some auto-documentation from your code, perhaps something like Doxygen (http://www.doxygen.nl/) could do the job for you?
I wondered how IceCream solves this problem. So I looked into the source code and came up with the following (slightly simplified) solution. It might not be 100% bullet-proof (e.g. I dropped get_text_with_indentation and I assume exactly one function argument), but it works well for different test cases. It does not need to parse source code itself, so it should be more robust and simpler than previous solutions.
#!/usr/bin/env python3
import inspect
from executing import Source
def func(var):
callFrame = inspect.currentframe().f_back
callNode = Source.executing(callFrame).node
source = Source.for_frame(callFrame)
expression = source.asttokens().get_text(callNode.args[0])
print(expression, '=', var)
i = 1
f = 2.0
dct = {'key': 'value'}
obj = type('', (), {'value': 42})
func(i)
func(f)
func(s)
func(dct['key'])
func(obj.value)
Output:
i = 1
f = 2.0
s = string
dct['key'] = value
obj.value = 42
Update: If you want to move the "magic" into a separate function, you simply have to go one frame further back with an additional f_back.
def get_name_of_argument():
callFrame = inspect.currentframe().f_back.f_back
callNode = Source.executing(callFrame).node
source = Source.for_frame(callFrame)
return source.asttokens().get_text(callNode.args[0])
def func(var):
print(get_name_of_argument(), '=', var)
If you want to get the caller params as in #Matt Oates answer answer without using the source file (ie from Jupyter Notebook), this code (combined from #Aeon answer) will do the trick (at least in some simple cases):
def get_caller_params():
# get the frame object for this function call
thisframe = inspect.currentframe()
# get the parent calling frames details
frames = inspect.getouterframes(thisframe)
# frame 0 is the frame of this function
# frame 1 is the frame of the caller function (the one we want to inspect)
# frame 2 is the frame of the code that calls the caller
caller_function_name = frames[1][3]
code_that_calls_caller = inspect.findsource(frames[2][0])[0]
# parse code to get nodes of abstract syntact tree of the call
nodes = ast.parse(''.join(code_that_calls_caller))
# find the node that calls the function
i_expr = -1
for (i, node) in enumerate(nodes.body):
if _node_is_our_function_call(node, caller_function_name):
i_expr = i
break
# line with the call start
idx_start = nodes.body[i_expr].lineno - 1
# line with the end of the call
if i_expr < len(nodes.body) - 1:
# next expression marks the end of the call
idx_end = nodes.body[i_expr + 1].lineno - 1
else:
# end of the source marks the end of the call
idx_end = len(code_that_calls_caller)
call_lines = code_that_calls_caller[idx_start:idx_end]
str_func_call = ''.join([line.strip() for line in call_lines])
str_call_params = str_func_call[str_func_call.find('(') + 1:-1]
params = [p.strip() for p in str_call_params.split(',')]
return params
def _node_is_our_function_call(node, our_function_name):
node_is_call = hasattr(node, 'value') and isinstance(node.value, ast.Call)
if not node_is_call:
return False
function_name_correct = hasattr(node.value.func, 'id') and node.value.func.id == our_function_name
return function_name_correct
You can then run it as this:
def test(*par_values):
par_names = get_caller_params()
for name, val in zip(par_names, par_values):
print(name, val)
a = 1
b = 2
string = 'text'
test(a, b,
string
)
to get the desired output:
a 1
b 2
string text
Since you can have multiple variables with the same content, instead of passing the variable (content), it might be safer (and will be simpler) to pass it's name in a string and get the variable content from the locals dictionary in the callers stack frame. :
def displayvar(name):
import sys
return name+" = "+repr(sys._getframe(1).f_locals[name])
If it just so happens that the variable is a callable (function), it will have a __name__ property.
E.g. a wrapper to log the execution time of a function:
def time_it(func, *args, **kwargs):
start = perf_counter()
result = func(*args, **kwargs)
duration = perf_counter() - start
print(f'{func.__name__} ran in {duration * 1000}ms')
return result
How to properly call one method from another in python.
I get some data from the AWS S3 bucket after I want to sort this data and write it into a .txt.
import boto3
import string
import json
import collections
def handler(event, context):
print(f'Event: {event}')
s3 = boto3.resource('s3')
bucket = s3.Bucket(event["bucket"])
for obj in bucket.objects.all():
key = obj.key
body = obj.get()['Body'].read()
b = json.loads(body)
c = WordCorrection.create_duplicated_words_file(b)
# WordCorrection.create_duplicated_words_file(WordCorrection.word_frequency(
# WordCorrection.correct_words(b)))
# WordCorrection.spell_words(WordCorrection.dict_spell_words(WordCorrection.unrecognized_words_from_textrtact(b)))
return c
CONFIDENT_LEVEL = 98
class WordCorrection:
def correct_words(data):
spell = SpellChecker()
correct_words_from_amazon = []
for items in data['Blocks']:
if items['BlockType'] == "WORD" and items['Confidence'] > CONFIDENT_LEVEL and {items["Text"]} != spell.known([items['Text']]):
correct_words_from_amazon.append(items['Text'])
correct_words_from_amazon = [''.join(c for c in s if c not in string.punctuation) for s in
correct_words_from_amazon]
return correct_words_from_amazon
def word_frequency(self, correct_words_from_amazon):
word_counts = collections.Counter(correct_words_from_amazon)
word_frequency = {}
for word, count in sorted(word_counts.items()):
word_frequency.update({word: count})
return dict(sorted(word_frequency.items(), key=lambda item: item[1], reverse=True))
def create_duplicated_words_file(word_frequency):
with open("word_frequency.txt", "w") as filehandle:
filehandle.write(str(' '.join(word_frequency)))
I was trying to use self but I cannot see a good result, and from the reason I use
WordCorrection.create_duplicated_words_file(WordCorrection.word_frequency(WordCorrection.correct_words(b)))
but I'm in 100% sure that it is not correct, there is another way to call one method from another?
I think your trouble is the result of a misunderstanding about keywords/namespaces for modules vs classes.
Modules:
In python, files are modules so when you are inside of a file, all functions defined up to that point in the file are "in scope." So if I have two functions like this:
def func_foo():
return "foo"
def func_bar():
return func_foo() + "bar"
Then func_bar() will return "foobar".
Classes
When you define a class using the class keyword, that defines a new scope/namespace. It is considered proper (although technically not required) to use the word self as the first parameter to an instance method, and this refers to the instance the method is called upon.
For example:
class my_clazz:
def method_foo(self):
return "foo"
def method_bar(self):
return self.method_foo() + "bar"
Then if I have later in the file:
example = my_clazz()
ret_val = example.method_bar()
ret_val will be "foobar"
That said, because I did not really utilize object-oriented programming features in this example, the class definition was largely unnecessary.
Your Issue
So for your issue, it seems like your trouble is caused by what appears to be unnecessarily wrapping your functions inside a class definition. If you got rid of the class definition header and just made all of your functions in the module you would be able to use the calling techniques I used above. For more information on classes in Python I'd recommend reading here.
I'm making a programming language with Python. I want to be able to run functions by typing:
task $function:
log "Hey!"
and then you can call it by typing:
$function
Right now, I have this code:
def runFunction(self, f):
## Here's where I need help. How will you make a function that runs a function that doesn't exist in
## the code?
...
elif i == 'task':
self.string = line[5:]
self.output = self.string.replace('{', '')
self.function = self.output.replace('}', '')
...
elif i not in self.keywords and '$' in i:
if i == self.function:
self.runFunction(self.function)
What should I do to make a runFunction() function?
What you could do?
You could use python built in function called eval() which lets you evaluate expressions dynamically.
Solution
def runFunction(self, f):
eval(f)
Where f has to be a string
And if you want to create functions:
You could use exec() which can evaluate a string.
Demonstration:
exec("def myFunction(a,b): return a + b")
and use it like
eval("myFunction(1,2)")
Starting from a script foo.py find all functions that are in use in local source code (i.e not built-in or third party packages), recursively.
EDIT: I do not want to find recursive functions. I want to find all functions that are in use!
e.g. foo.py
import bar
def not_used():
pass
bar.do_stuff(x,y)
bar.py
import math
def more_stuff(x,y):
result = math.abs(-x+-y)
return result
def do_stuff(x,y):
more_stuff(x,y)
Should return do_stuff & more_stuff
Should ignore not_used & abs
Many thanks
EDIT: Code so far
import dis
py_file = 'foo.py'
with open(py_file) as file:
source_code = file.read()
compiled = compile(source_code, py_file, "exec")
funcs = []
byte_code = dis.Bytecode(compiled)
instructions = list(reversed([x for x in byte_code]))
for (ix, instruction) in enumerate(instructions):
if instruction.opname == "CALL_FUNCTION":
load_func_instr = instructions[ix + instruction.arg + 1]
funcs.append(load_func_instr.argval)
results = [f'{ix}: {funcname}'for (ix, funcname) in enumerate(reversed(funcs), 1)]
You can use Python's ast (abstract syntax tree) module
A short example:
import ast
code = """
import math
def more_stuff(x,y):
result = math.abs(-x+-y)
return result
def do_stuff(x,y):
more_stuff(x,y)
"""
tree = ast.parse(code)
funcs = [x for x in ast.walk(tree) if isinstance(x, ast.FunctionDef)]
print(', '.join(f.name for f in funcs))
prints:
more_stuff, do_stuff
now you can add the tests, you like. For example the SO question
How to find/detect if a build-in function is used in Python AST?
discusses how to detect if a function is being used.
I've declared a number of variables at the start of my script, as I'm using them in a number of different methods ("Functions" in python?). When I try to access them, I can't seem to get their value = or set them to another value for that matter. For example:
baseFile = open('C:/Users/<redacted>/Documents/python dev/ATM/Data.ICSF', 'a+')
secFile = open('C:/Users/<redacted>/Documents/python dev/ATM/security.ICSF', 'a+')
def usrInput(raw_input):
if raw_input == "99999":
self.close(True)
else:
identity = raw_input
def splitValues(source, string):
if source == "ident":
usrTitle = string.split('>')[1]
usrFN = string.split('>')[2]
usrLN = string.split('>')[3]
x = string.split('>')[4]
usrBal = Decimal(x)
usrBalDisplay = str(locale.currency(usrBal))
elif source == "sec":
usrPIN = string.split('>')[1]
pinAttempts = string.split('>')[2]
def openAccount(identity):
#read all the file first. it's f***ing heavy but it'll do here.
plString = baseFile.read()
xList = plString.split('|')
parm = str(identity)
for i in xList:
substr = i[0:4]
if parm == substr:
print "success"
usrString = str(i)
else:
lNumFunds = lNumFunds + 1
splitValues("ident", usrString)
When I place baseFile and secFile in the openAccount method, I can access the respective files as normal. However, when I place them at the root of the script, as in the example above, I can no longer access the file - although I can still "see" the variable.
Is there a reason to this? For reference, I am using Python 2.7.
methods ("Functions" in python?)
"function" when they "stand free"; "methods" when they are members of a class. So, functions in your case.
What you describe does definitely work in python. Hence, my diagnosis is that you already read something from the file elsewhere before you call openAccount, so that the read pointer is not at the beginning of the file.