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Update Python dictionary while looping

I was trying to iterate over a list of values, craft a dictionary to save each value in a structured way, and then append the dictionary to a new list of results, but I found an unexpected behavior.
Below is an example:
values_list = [1,2,3]
# Basic dict
result_dict = {
'my_value': ''
}
# Iterate, craft a dictionary, and append result
dicts_list = []
for value in values_list:
result_dict.update({'my_value': value})
dicts_list.append(result_dict)
print(dicts_list)
As you can see, first I create a basic dictionary, then I'm iterating over the list of values and updating the dictionary, at the end I'm appending the crafted dictionary to a separate list of results (dicts_list).
As a result I was expecting:
[{'my_value': 1}, {'my_value': 2}, {'my_value': 3}]
but instead I was getting:
[{'my_value': 3}, {'my_value': 3}, {'my_value': 3}]
It looks like every iteration is not only updating the basic dictionary – which is expected – but also the dictionaries already appended to the list of results on the previous iteration.
To fix the issue, I nested the basic dictionary under the for loop:
values_list = [1,2,3]
# Iterate, craft a dictionary, and append result
dicts_list = []
for value in values_list:
result_dict = {'my_value': ''}
result_dict.update({'my_value': value})
dicts_list.append(result_dict)
print(dicts_list)
Can anyone explain what is wrong with the first approach? How is the loop causing the list of appended dictionaries to be updated?
Thanks for any advice! :)
Franz

As explained in the comment, you're appending the same dictionary in each iteration because update() modifies the result_dict rather than returning a copy. So, the only change you need to do is to append a copy of the crafted dictionary. For example:
values_list = [1,2,3]
# Basic dict
result_dict = {
'my_value': ''
}
# Iterate, craft a dictionary, and append result
dicts_list = []
for value in values_list:
result_dict.update({'my_value': value})
dicts_list.append(dict(result_dict)) # <--- this is the only change
print(dicts_list)

To gain understanding of How is the loop causing the list of appended dictionaries to be updated? you can use Python Tutor: Visualize code in Python with the code you provided in your question to see the effect of executing the code line by line with the final result being following visualization:
I suggest you read also Facts and myths about Python names and values.

python updating dictionary with list as the value type

I'm trying to iterate through data extracted from a file and store them in a dictionary based on each data's id
These are the id (str) for the data : "sensor", "version", "frame", "function"
And the data are in hexadecimal string.
What I bascially start with is a huge list of tuples in a form of id and data (that i extracted from a file)
example_list = [("sensor", 245), ("frame", 455), ("frame", 77)] and so on
This example_list stores all the data, so it has information of data for all the id.
I want to make a dictionary with id as key and list of data as value so when done iterating through the example_list, I have list of values for specific id (so I can iterate through the value list to get all the data for a specific id (the key))
To start, all values (list) will start with an empty list
my_dict = {"sensor": [], "frame": [], "version": [], "function": []}
Then, as I iterate through example_list, if the id is in my_dict as a key, I append the value to the values list in my_dict
for itm in example_list:
if itm[0] in my_dict:
tmp = my_dict[itm[0]] # since itm[0] is the id
tmp.append(itm[1])
my_dict[itm[0]] = tmp # update the list
When I tried this, it seems like the final my_dict's value list has the value of the lastest data
What I mean by this is if
example_list = [("sensor", 245), ("frame", 455), ("frame", 77)]
then
my_dict = {"sensor": [245], "frame": [77], "version": [], "function": []}
I may be wrong about this interpretation (since the data I'm reading is really big), but when I printed my_dict in the end of function, each value list had only one data inside, which is far off from what I expected (list of data instead of just one)
I tried searching and people used update function to update the dictionary but that one also didn't seem to work and gave me somehting unhashable error/warning.
Any way to implement what I want to do?

try doing it like so:
for itm in example_list:
if itm[0] in my_dict:
my_dict[itm[0]].append(itm[1])

Your code is working as required. To simplify, as you've already instantiated the dict with empty lists:
for i,j in example_list:
my_dict[i].append(j)
print(my_dict)
Output:
{'sensor': [245], 'frame': [455, 77], 'version': [], 'function': []}

What you want to do is:
for itm in example_list:
if itm[0] in my_dict.keys(): # have to look if keys match
my_dict[itm[0]].append(itm[1]) # # directly access the key-value pair
Your problem was that you created a new list and appended your item to it each time the loop was run, therefore the old data was deleted everytime.

Check for string in list items using list as reference

I want to replace items in a list based on another list as reference.
Take this example lists stored inside a dictionary:
dict1 = {
"artist1": ["dance pop","pop","funky pop"],
"artist2": ["chill house","electro house"],
"artist3": ["dark techno","electro techno"]
}
Then, I have this list as reference:
wish_list = ["house","pop","techno"]
My result should look like this:
dict1 = {
"artist1": ["pop"],
"artist2": ["house"],
"artist3": ["techno"]
}
I want to check if any of the list items inside "wishlist" is inside one of the values of the dict1. I tried around with regex, any.
This was an approach with just 1 list instead of a dictionary of multiple lists:
check = any(item in artist for item in wish_list)
if check == True:
artist_genres.clear()
artist_genres.append()
I am just beginning with Python on my own and am playing around with the SpotifyAPI to clean up my favorite songs into playlists. Thank you very much for your help!

The idea is like this,
dict1 = { "artist1" : ["dance pop","pop","funky pop"],
"artist2" : ["house","electro house"],
"artist3" : ["techno","electro techno"] }
wish_list = ["house","pop","techno"]
dict2={}
for key,value in dict1.items():
for i in wish_list:
if i in value:
dict2[key]=i
break
print(dict2)

A regex is not needed, you can get away by simply iterating over the list:
wish_list = ["house","pop","techno"]
dict1 = {
"artist1": ["dance pop","pop","funky pop"],
"artist2": ["chill house","electro house"],
"artist3": ["dark techno","electro techno"]
}
dict1 = {
# The key is reused as-is, no need to change it.
# The new value is the wishlist, filtered based on its presence in the current value
key: [genre for genre in wish_list if any(genre in item for item in value)]
for key, value in dict1.items() # this method returns a tuple (key, value) for each entry in the dictionary
}
This implementation relies a lot on list comprehensions (and also dictionary comprehensions), you might want to check it if it's new to you.

Extracting values from old dictionary into new dictinary using iteration

I am struggling to figure out an assignment.
The problem set up is:
I have a list containing ratios ( unique_ratio = ['0.05', '0.98', '1.45']
I have a dictionary containing k:v as ratio:count the number of times ratio has appeared in a previous variable ( dict = {'0.05':'5', '0.32':'72', '0.98': '21'}
I want to iterate over the dictionary and extract the k:v for the ratios which appear in the unique_ratio list. I want to store these k:v's in a new dictionary (frequencies = {})
I am running pytho 3.7
I have tried iterating over the dictionary using for loop but am never able to extract the k:v pair.
I am unsure whether I should test for i in unique_ratios or i in dict
for i in dict.values():
frequencies = { k:v for k,v in comp_dict_count.items() if 'i' in
unique_ratios }
print(frequencies)
Everything I have tried has led to syntax errors. The above code leads to empty frequencies dictionary.

You need a single dictionary comprehension for this. Also for a better formormance you could check membership using sets, reducing the lookup complexity to O(1):
unique_ratio = set(['0.05', '0.98', '1.45'])
d = {'0.05':'5', '0.32':'72', '0.98': '21'}
{k:v for k,v in d.items() if k in unique_ratio}
# {'0.05': '5', '0.98': '21'}

Update dictionary if in list

I'm running through an excel file reading line by line to create dictionaries and append them to a list, so I have a list like:
myList = []
and a dictionary in this format:
dictionary = {'name': 'John', 'code': 'code1', 'date': [123,456]}
so I do this: myList.append(dictionary), so far so good. Now I'll go into the next line where I have a pretty similar dictionary:
dictionary_two = {'name': 'John', 'code': 'code1', 'date': [789]}
I'd like to check if I already have a dictionary with 'name' = 'John' in myList so I check it with this function:
def checkGuy(dude_name):
return any(d['name'] == dude_name for d in myList)
Currently I'm writing this function to add the guys to the list:
def addGuy(row_info):
if not checkGuy(row_info[1]):
myList.append({'name':row_info[1],'code':row_info[0],'date':[row_info[2]]})
else:
#HELP HERE
in this else I'd like to dict.update(updated_dict) but I don't know how to get the dictionary here.
Could someone help so dictionary appends the values of dictionary_two?

I would modify checkGuy to something like:
def findGuy(dude_name):
for d in myList:
if d['name'] == dude_name:
return d
else:
return None # or use pass
And then do:
def addGuy(row_info):
guy = findGuy(row_info[1])
if guy is None:
myList.append({'name':row_info[1],'code':row_info[0],'date':[row_info[2]]})
else:
guy.update(updated_dict)

This answer suggestion is pasted on the comments where it was suggested that if "name" is the only criteria to search on then it could be used as a key in a dictionary instead of using a list.
master = {"John" : {'code': 'code1', 'date': [123,456]}}
def addGuy(row_info):
key = row_info[1]
code = row_info[0]
date = row_info[2]
if master.get(key):
master.get(key).update({"code": code, "date": date})
else:
master[key] = {"code": code, "date": date}

If you dict.update the existing data each time you see a repeated name, your code can be reduced to a dict of dicts right where you read the file. Calling update on existing dicts with the same keys is going to overwrite the values leaving you with the last occurrence so even if you had multiple "John" dicts they would all contain the exact same data by the end.
def read_file():
results = {name: {"code": code, "date": date}
for code, name, date in how_you_read_into_rows}
If you actually think that the values get appended somehow, you are wrong. If you wanted to do that you would need a very different approach. If you actually want to gather the dates and codes per user then use a defauldict appending the code,date pair to a list with the name as the key:
from collections import defaultdict
d = defaultdict(list)
def read_file():
for code, name, date in how_you_read_into_rows:
d["name"].append([code, date])
Or some variation depending on what you want the final output to look like.