python recursively merge dictionaries

As a placeholder, we could just wrap the two values in a tuple: We can easily modify the leaf-merging rule, for example: We could also potentially clean this up by using a third-party library to dispatch based on the type of the inputs. How to handle repondents mistakes in skip questions? Think you can improve upon the dict_merge For Python 3, iteritems() is not available anymore in dicts, and one can simply use items() instead. Based upon these and other answers I came up with this code: My use case is merging YAML files where I only have to deal with a subset of possible data types. Apparently dict(x, **y) is going around as "cool hack" for "call How can I remove a key from a Python dictionary? # distributed under the License is distributed on an "AS IS" BASIS. You switched accounts on another tab or window. In that light, I present the following: There will be a new option when Python 3.8 releases (scheduled for 20 October, 2019), thanks to PEP 572: Assignment Expressions. In the example, just. A nice way of defining an appropriate recursive merger function f is using multipledispatch which allows to define functions that evaluate along different paths depending on the type of their arguments. Can I use the door leading from Vatican museum to St. Peter's Basilica? It will also work for other ("dict-like") mappings. Behind the scenes with the folks building OverflowAI (Ep. The only real advantage to the assignment expression approach occurs if: This can be done with a single dict comprehension: In my view the best answer for the 'single expression' part as no extra functions are needed, and it is short. Ask Question Asked 13 years, 2 months ago Modified 1 year, 10 months ago Viewed 132k times 106 d3 = dict (d1, **d2) I understand that this merges the dictionary. If you need this try the answer of @Osiloke below: they are directory structures so i don't think s/he wants anything flattened? Different Ways to Merge Dictionaries Before Python 3.9 d1.update (d2) Update the dictionary with the key/value pairs from , overwriting existing keys. Are arguments that Reason is circular themselves circular and/or self refuting? TypeError: unsupported operand type(s) for +: 'dict_items' and 'dict_items', How to merge multiple json objects into a single json object using python. Deleting an executable on the path doesn't preclude another executable with the same name further upstream. The problem itself isnt too It divides input array in two halves, calls itself for the two halves and then merges the two sorted halves. How do I check whether a file exists without exceptions? Again, it doesn't work for 3 when keys are not strings. But, is it unique? The only minor problem is that it doesn't make completely obvious that values from y takes precedence over values from x, but I don't believe it's difficult to figure that out. I had no clue this existed -- plus it was a fun little thing to code :-), @agf: Correct, so it seems OP needs solution employing recurrence. In some of the solutions here the returned dict contains references to the input dicts. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Something like this should do: def merge(d1, d2): for k in d2: if k in d1 and isinstance(d1[k], dict) and isinstance(d2[k], dict): merge(d1[k], d2[k]) else: d1[k] = d2[k] 0. 1 Answer Sorted by: 12 First of all, there is a bug in the code - if an array is empty, you'll get a "maximum recursion depth exceeded" error. The merge itself accounts for key conflicts, and instead of overwriting data from a dictionary further down the merge chain, it creates a set of values and appends to that; no data is lost. There are various ways in which Dictionaries can be merged by the use of various functions and constructors in Python. python. def iterdict(d): for k,v in d.items(): if isinstance(v, dict): iterdict(v) else: print (k,":",v) iterdict(D1) Output When the initial dictionary object is passed to this function, all the key-value pairs are traversed. How to Flatten a Dictionary in Python in 4 Different Ways why does this code use collections.Mapping instead of dict type? Why this happens? Also, Raymond Hettinger's Chainmap answer is pretty elegant, since it can take an arbitrary number of dicts as arguments, but from the docs it looks like it sequentially looks through a list of all the dicts for each lookup: Lookups search the underlying mappings successively until a key is found. Alaska mayor offers homeless free flight to Los Angeles, but is Los Angeles (or any city in California) allowed to reject them? Here's an easy way to do it using generators: One issue with this question is that the values of the dict can be arbitrarily complex pieces of data. Can a judge or prosecutor be compelled to testify in a criminal trial in which they officiated? If you have two or more lists of dictionaries and want to combine them into a list of merged dictionaries, where the dictionaries are merged by an attribute, you can use the lists_mergeby filter. Iterating over dictionaries using 'for' loops. theres enough meat to it that people who just hack at stuff might solve Overwrite string with dict from enhancer. which makes the code simpler to reason about and test. 594), Stack Overflow at WeAreDevelopers World Congress in Berlin, Temporary policy: Generative AI (e.g., ChatGPT) is banned, Preview of Search and Question-Asking Powered by GenAI, Merge a nested dictionary (default values), Merge two dictionaries and persist the values of first dictionaries. This normally Some answers also considered dicts that contain lists e.g. Do you think this might be a coincidence? I just use a simple helper function to solve the problem: The problem I have with solutions listed to date is that, in the merged dictionary, the value for key "b" is 10 but, to my way of thinking, it should be 12. In 3.5 and above {**x,**y} gives the concatenated dictionary, New! trying to merge, New! the ** mechanism. if val is not dict then update from enhancing dict. It returns None (you can always add return d if you prefer) as it updates dict d in-place. This one also avoids mutation/side effects: This is a solution I made that recursively merges dictionaries to an infinite depth. Thinking of it, maybe the name is misleading, as it might evoke a deepcopy, which it does not provide. yes, reduce would be good. my answer to the canonical question on a "Dictionaries of dictionaries merge", Answer on how to add new keys to a dictionary, Modern Python Dictionaries, A Confluence of Great Ideas, Works fine in Python 3 and PyPy and PyPy 3, https://mathieularose.com/how-not-to-flatten-a-list-of-lists-in-python/, Behind the scenes with the folks building OverflowAI (Ep. A warning to everyone looking for solutions: This question is about nested dicts only. To merge two nested dicts simply use merge(f) e.g. Improve your base case handling: if len (array) <= 1: return array Other improvements: Since dictviews support set operations, I was able to greatly simplify jterrace's answer. While the question has already been answered several times, A new syntax for this, proposed in PEP 448 and available as of Python 3.5, is. is expected to pass. python: merging dictionaries by identical value of key, How to merge 2 dictionaries in Python by single value. Are the NEMA 10-30 to 14-30 adapters with the extra ground wire valid/legal to use and still adhere to code? rev2023.7.27.43548. Python: Python: How to recursively merge 2 dictionaries? Merge Sort is a Divide and Conquer algorithm. python recursively merge dictionaries - Code Examples & Solutions To subscribe to this RSS feed, copy and paste this URL into your RSS reader. I got keys as values in the combined dict. Code examples. How to merge two dictionaries with the same keys? This assumes your list of dicts are the same length. Well, if people insist on making it a oneliner, you can always do, @AlexanderOh I am not sure whenever this is a joke or not; I see this as a perfectly (valid) answ! python Yes this is definetly less rows in code but it is not effective. Hope that helps. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing, New! Were all of the "good" terminators played by Arnold Schwarzenegger completely separate machines? The mentioned one-expression-solutions are either slow or evil. For items with keys in both dictionaries ('b'), you can control which one ends up in the output by putting that one last. The new assignment expression operator := allows you to assign the result of the copy and still use it to call update, leaving the combined code a single expression, rather than two statements, changing: while behaving identically in every way. Ill leave the details of how I go about interviewing people for another October 19, 2019 / dictionary, Python / By Varun In this article we will discuss different ways to merge two or more dictionaries. python - Bug in recursive dict-merging function - Stack Overflow The desired output on level_2_a can be a single level list. It works OK for on-site Combine two dictionaries with preference to one of them -. How to Merge two or more Dictionaries in Python ? This can be done using the following lines of code: dict1.update (dict2) The complete code would be as follows : Wow! I need to merge multiple dictionaries, here's what I have for instance: With A B C and D being leaves of the tree, like {"info1":"value", "info2":"value2"}, There is an unknown level(depth) of dictionaries, it could be {2:{"c":{"z":{"y":{C}}}}}. frozensets or tuples), but this method fails in Python 3 when keys are not strings. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Lists, dicts and tuples should be traversed recursively. November 18, 2021 In this tutorial, you'll learn how to use Python to merge dictionaries. I originally coded up the python version for Perhaps the most common way is to make use of the `update()`python method which allows values from one dictionary to be loaded into another dictionary: `d1.update(d2)`python. I've had to remove the curly braces around the letters and put them in single quotes for this to be legit Python (else they would be set literals in Python 2.7+) as well as append a missing brace: Which matches the desired outcome of the original question (after changing, e.g. as Tony does, but (not surprisingly) the difference in notation turns out not to have any measurable effect on performance. "Sibi quisque nunc nominet eos quibus scit et vinum male credi et sermonem bene", Heat capacity of (ideal) gases at constant pressure, Story: AI-proof communication by playing music, The British equivalent of "X objects in a trenchcoat". For dictionaries x and y, their shallowly-merged dictionary z takes values from y, replacing those from x. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing, Strings only limitation for keywords expansion is enough to rule out. Why would a highly advanced society still engage in extensive agriculture? Making statements based on opinion; back them up with references or personal experience. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. enough of them so that the code you get back has a decent chance of To create z: If you use Python version 3.9.0a4 or greater, you can directly use: Note: this has become a popular answer, but it is important to point out that if y has any non-string keys, the fact that this works at all is an abuse of a CPython implementation detail, and it does not work in Python 3, or in PyPy, IronPython, or Jython. I see only issue what if key is missing in target dictionary? In that Recursively Merge Dictionaries in Python | XOR Media I have another slightly different solution here: By default it resolves conflicts in favor of values from the second dict, but you can easily override this, with some witchery you may be able to even throw exceptions out of it. Learn more about Teams This does not answer the question. IFF all your keys are guaranteed to be strings, this is a fully supported option. The downside to this is that it makes Link to this answer Share Copy Link . 3 A warning to everyone looking for solutions: This question is about nested dicts only. Just removed the error handling. : Despite what Guido says, dict(x, **y) is in line with the dict specification, which btw. Can a judge or prosecutor be compelled to testify in a criminal trial in which they officiated? Also, Guido is not a fan. You can always run it through more vigorous tests once How do I merge two dictionaries in a single expression in Python? difficult, but it will require a bit of mental effort to solve it and Python: How to recursively merge 2 dictionaries? [duplicate] rev2023.7.27.43548. Breaking it down line-by-line, the initial if handles the case where Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing, What do you want for your arbitrary depth of dictionaries? The British equivalent of "X objects in a trenchcoat". Not the answer you're looking for? If the key, k, is For me a sensible merge logic means. For dictionaries x and y, their shallowly-merged dictionary z takes values from y, replacing those from x. python - How to merge dictionaries of dictionaries? - Stack Overflow Dictionaries are intended to take hashable keys (e.g. I am having lists of dicts in my structures all the time, the other solutions cannot properly merge this. Not the answer you're looking for? Now lists will be merged, checks and raises an exception if both dicts have a key in common but different data types, and the method takes 2 or more dicts to merge instead of just two. It's also more extensible, as merging three dicts is obvious: where using assignment expressions won't scale like that; the closest you could get would be: or without the temporary tuple of Nones, but with truthiness testing of each None result: either of which is obviously much uglier, and includes further inefficiencies (either a wasted temporary tuple of Nones for comma separation, or pointless truthiness testing of each update's None return for or separation). They will be much less performant than copy and update or the new unpacking because they iterate through each key-value pair at a higher level of abstraction, but they do respect the order of precedence (latter dictionaries have precedence). python recursively merge dictionaries Comment . Don't use what you see in the formerly accepted answer: In Python 2, you create two lists in memory for each dict, create a third list in memory with length equal to the length of the first two put together, and then discard all three lists to create the dict. Instead, you can use a tuple display and index, which works regardless of what the first element evaluates to (although it's not quite as pretty): If you don't have x in a variable yet, you can use lambda to make a local without using an assignment statement. It might not be the most effecient on the page, but it's the most thorough and you're not going to lose any information when you merge your 2 to N dicts. Connect and share knowledge within a single location that is structured and easy to search. The implicit calling contract is that namespaces take ordinary dictionaries, while users must only pass keyword arguments that are strings. Were all of the "good" terminators played by Arnold Schwarzenegger completely separate machines? Abuse leading to a one-expression solution for Matthew's answer: You said you wanted one expression, so I abused lambda to bind a name, and tuples to override lambda's one-expression limit. GitHub Instantly share code, notes, and snippets. spend a bit more time setting it up and you have lots of examples about In that situation its best to set up a OverflowAI: Where Community & AI Come Together, How to recursively explore python nested dictionaries? How do I merge two dictionaries in a single expression in Python?

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