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1. Top results related to how to create a dictionary

   • How to create a dictionary where the keys are all the week numbers within a year and values as lists of the dates of each weekday within a week?

     Top Answer

     Answered May 25, 2019 · 3 votes

     I'd iterate over the days in a year and then add them to a list for each week number. If you use defaultdict, you can do that without having to initialize the dict for the week numbers:

     import datetimefrom collections import defaultdict-date = datetime.date(2019, 1, 1)enddate = datetime.date(2019, 12, 31)days_in_each_week = defaultdict(list)while date < enddate: days_in_each_week[date.isocalendar()[1]].append(date.strftime("%d/%m/%Y")) date += datetime.timedelta(days=1)print(days_in_each_week)

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     1/5

   • How to create a dictionary to cache values in python?

     Top Answer

     Answered Oct 29, 2021 · 1 votes

     If you want to save the dict between uses of your function, you can't define it as a local variable. Otherwise, it disappears when the function ends, and is created all-new at the next call, without saving previously encountered values.

     Here are three ways to do this, using an object attribute, a default argument, or a decorator from module functools. I used the Fibonacci function rather than the Collatz sequence, so as not to spoil the problem completely for you. I tested the cached Fibonacci functions by trying to compute fib(40). A bad implementation of Fibonacci without caching would take an awfully long time to compute fib(40); the three functions below return the result immediately.

     # FIRST WAY: using an object attributedef fib1(n): if n in fib1.cache: return fib1.cache[n] else: fib1.cache[n] = fib1(n-2) + fib1(n-1) return fib1.cache[n]fib1.cache = {0: 0, 1: 1}print(fib1(11))# 89print(fib1(40))# 102334155# SECOND WAY: using a default argumentdef fib2(n, cache={0: 0, 1: 1}): if n in cache: return cache[n] else: cache[n] = fib2(n-2) + fib2(n-1) return cache[n]print(fib2(11))# 89print(fib2(40))# 102334155

     However, there is a third way. Since caching values is not particularly original and is often useful, you can use functools.cache to automatically cache the outputs of a function:

     • Documentation on functools.cache

     import functools-@functools.cachedef fib3(n): if n == 0 or n == 1: return n else: return fib3(n-2) + fib3(n-1)print(fib3(11))# 89print(fib3(40))# 102334155

     For contrast, here is the bad way that doesn't properly save the cache from one call to the next:

     # BAD WAY: Don't do this. The cache is local to each call, and erased as soon as the function returns.def fib0(n): cache = {0: 0, 1: 1} if n in cache: return cache[n] else: cache[n] = fib0(n-2) + fib0(n-1) return cache[n]print(fib0(11))# 89print(fib0(40))# TAKES AWFULLY LONG TIME

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   • How to create a dictionary from a list of dictionary using specific keys in Python

     Top Answer

     Answered Apr 03, 2021 · 3 votes

     Try to use:

     d2 = [{"c": 3, "a": 1, "b": 2, "d": 4}, {"a": 100, "c": 300, "b": 200, "d": 400}, {"b": 'Ball', "c": 'Cat', "d": 'Doll', "a": 'Apple'}]-filter_list = ["a", "c"]d22 = [{k: d[k] for k in filter_list} for d in d2]print(d22)

     Print:

     [{'a': 1, 'c': 3}, {'a': 100, 'c': 300}, {'a': 'Apple', 'c': 'Cat'}]-

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     3/5

   • How to create a dictionary to reverse lookup list items that each have sets?

     Top Answer

     Answered Mar 27, 2019 · 2 votes

     A straightforward looping solution using collections.defaultdict

     from collections import defaultdictd = defaultdict(set)for k,v in series.items(): for prop in v: d[prop].add(k)print(d)#defaultdict(set,# {'black': {'test2', 'test3'},# 'blue': {'test1', 'test2'},# 'green': {'test3'},# 'orange': {'test1'},# 'red': {'test2'},# 'yellow': {'test1', 'test3'}})

     Another approach using pandas

     First convert series into a DataFrame:

     import pandas as pddf = pd.DataFrame({k: list(v) for k, v in series.items()})print(df)# test1 test2 test3#0 blue blue black#1 orange black green#2 yellow red yellow

     Next melt

     the DataFrame, groupby the value and use set as the aggregate function:

     print(pd.melt(df).groupby("value", as_index=True).agg(set))# variable#value #black {test3, test2}#blue {test1, test2}#green {test3}#orange {test1}#red {test2}#yellow {test1, test3}

     Finally to go back to a dictionary, call to_records() and apply the dict constructor:

     print(dict(pd.melt(df).groupby("value", as_index=True).agg(set).to_records()))#{'black': {'test2', 'test3'},# 'blue': {'test1', 'test2'},# 'green': {'test3'},# 'orange': {'test1'},# 'red': {'test2'},# 'yellow': {'test1', 'test3'}}

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   • Also try

     how to create a dictionary in python	how to create a dictionary from a list in python
     how to create a dictionary from two lists	how to create a dictionary in c++
     how to create a dictionary app	how to create a dictionary in microsoft word
     how to create a dictionary in javascript	how to create a dictionary in c#

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2. www.geeksforgeeks.org › how-to-create-a-dictionaryHow to create a Dictionary in Python - GeeksforGeeks

   www.geeksforgeeks.org › how-to-create-a-dictionary

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   Jul 4, 2023 · In Python, a dictionary can be created by placing a sequence of elements within curly {} braces, separated by a ‘comma’. Let us see a few examples to see how we can create a dictionary in Python. Define a Dictionary with Items.

3. www.freecodecamp.org › news › create-a-dictionary-inCreate a Dictionary in Python – Python Dict Methods

   www.freecodecamp.org › news › create-a-dictionary-in

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   Mar 14, 2022 · How to Create a Dictionary in Python. A dictionary in Python is made up of key-value pairs. In the two sections that follow you will see two ways of creating a dictionary. The first way is by using a set of curly braces, {}, and the second way is by using the built-in dict() function.

4. python.land › python-data-types › dictionariesPython Dictionary: How To Create And Use, With Examples

   python.land › python-data-types › dictionaries

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   Jul 14, 2023 · Learn everything there is to know about the Python dictionary, like how to create one, how to add elements to it, and how to retrieve them.

5. www.w3schools.com › python › python_dictionariesPython Dictionaries - W3Schools

   www.w3schools.com › python › python_dictionaries

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   Dictionaries are used to store data values in key:value pairs. A dictionary is a collection which is ordered*, changeable and do not allow duplicates. As of Python version 3.7, dictionaries are ordered. In Python 3.6 and earlier, dictionaries are unordered.

   Code sample

   thisdict ={

     "brand": "Ford",

     "model": "Mustang",

     "year": 1964

   }...

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6. learnpython.com › blog › create-dictionary-in-python5 Ways to Create a Dictionary in Python | LearnPython.com

   learnpython.com › blog › create-dictionary-in-python

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   • Python Dictionary From the Dictionary Literal {} Not surprisingly, this is the most common method for creating dictionaries in Python. All you have to do is declare your key-value pairs directly into the code and remember to use the proper formatting
   • Python Dictionary From the dict() Constructor. Dictionaries can also be built from the Python dict() constructor. dict() is a built-in function in Python, so it is always available to use without the need to import anything.
   • Python Dictionary From a JSON File. JSON stands for JavaScript Object Notation, and it is an extremely common file format for storing and transmitting data on the web.
   • Python Dictionary From Two Dictionaries Using the Dictionary Union Operator. If you’re using Python version 3.9 or greater, there’s yet another way to create a dictionary in Python: the dictionary union operator (|), introduced in Python 3.9.

7. note.nkmk.me › en › python-dict-createCreate a dictionary in Python ({}, dict(), dict comprehensions)

   note.nkmk.me › en › python-dict-create

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   Aug 21, 2023 · In Python, you can create a dictionary (dict) with curly brackets {}, dict(), and dictionary comprehensions. Contents Create a dictionary with curly brackets {}

8. People also ask

   How to create a dictionary in Python?

   • In Python, a dictionary can be created by placing a sequence of elements within curly {} braces, separated by a ‘comma’. Let us see a few examples to see how we can create a dictionary in Python. In this example, we first declared an empty dictionary D, then added the elements from the Python list L into the dictionary.

   How to create a Dictionary in Python - GeeksforGeeks

   www.geeksforgeeks.org/how-to-create-a-dictionary-in-python/

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   How do you create a dictionary?

   • A dictionary is created by using curly braces. Inside these braces, we can add one or more key-value pairs. The pairs are separated by commas when adding more than one key-value pair. The first dictionary in our example associates keys (names like Jack and Pete) with values (their phone numbers). The second dictionary is an empty one.

   Python Dictionary: How To Create And Use, With Examples

   python.land/python-data-types/dictionaries

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   How do dictionaries work in Python?

   • In Python 3.6 and earlier, dictionaries are unordered. Dictionaries are written with curly brackets, and have keys and values: Create and print a dictionary: Dictionary items are ordered, changeable, and do not allow duplicates. Dictionary items are presented in key:value pairs, and can be referred to by using the key name.

   Python Dictionaries - W3Schools

   www.w3schools.com/python/python_dictionaries.asp

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   How to create a dictionary using dict() function?

   • The dict() function builds a dictionary from a sequence or list of key-value pairs ( tuples ): Analogous to list comprehensions, you can also use dictionary comprehensions to create a new dictionary. While a list only contains values, a dictionary contains key/value pairs. Hence, dictionary comprehensions need to define both.

   Python Dictionary: How To Create And Use, With Examples

   python.land/python-data-types/dictionaries

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9. stackabuse.com › python-dictionary-tutorialGuide to Dictionaries in Python - Stack Abuse

   stackabuse.com › python-dictionary-tutorial

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   Aug 31, 2023 · How To Create a Dictionary in Python. To create a Python dictionary, we pass a sequence of items (entries) inside curly braces {} and separate them using a comma (,). Each entry consists of a key and a value, also known as a key-value pair.