- Python Create Dictionary From List Of Variables In Research Science
- Create Dictionary From List Of Tuples
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With Python, creating and using a dictionary is much like working with a list, except that you must now define a key and value pair. Here are the special rules for creating a key:
The key must be unique. When you enter a duplicate key, the information found in the second entry wins — the first entry is simply replaced with the second.
This tutorial will demonstrate the use of both class and instance variables in object-oriented programming in Python. The dictionary is Python’s built-in mapping type. Modules are Python.py files that consist of Python code. They can create function definitions and statements that you can reference in other Python.py files or via. [Python] trying to create a dictionary in python, using variables as a value; Ronrsr. Nov 20, 2006 at 7:40 am: but I keep getting syntax errors on this one. Creating dictionarie names, using variables? Environment variables in cgi; Finding lowest value in dictionary of objects, how?
Python Overview Python Built-in Functions Python String Methods Python List Methods Python Dictionary Methods Python. Creating Variables. Rules for Python. A Beginner's Python Tutorial/Tuples, Lists, Dictionaries. From Wikibooks, open books for an open world. When you initially create a dictionary, it is very much like making a tuple or list. Tuples have ( and ) things, lists have [ and ] things. Variable, or entry in a list or dictionary (An entry in a dictionary is just a variable with a. A common way to create a dictionary from two lists is zipping. The zip built in takes two lists and creates a list of pairs from them. In turn, a list of pairs can be used to create a dictionary directly.
The key must be immutable. This rule means that you can use strings, numbers, or tuples for the key. You can’t, however, use a list for a key.
You have no restrictions on the values you provide. A value can be any Python object, so you can use a dictionary to access an employee record or other complex data. The following steps help you understand how to use dictionaries better.
1Open a Python Shell window.
You see the familiar Python prompt.
2Type Colors = {“Sam”: “Blue”, “Amy”: “Red”, “Sarah”: “Yellow”} and press Enter.
Python creates a dictionary containing three entries with people’s favorite colors. Notice how you create the key and value pair. The key comes first, followed by a colon and then the value. Each entry is separated by a comma.
3Type Colors and press Enter.
You see the key and value pairs. However, notice that the entries are sorted in key order. A dictionary automatically keeps the keys sorted to make access faster, which means that you get fast search times even when working with a large data set. The downside is that creating the dictionary takes longer than using something like a list because the computer is busy sorting the entries.
4Type Colors[“Sarah”] and press Enter.
You see the color associated with Sarah, Yellow. Using a string as a key, rather than using a numeric index, makes the code easier to read and makes it self-documenting to an extent.
By making your code more readable, dictionaries save you considerable time in the long run (which is why they’re so popular). However, the convenience of a dictionary comes at the cost of additional creation time and a higher use of resources, so you have trade-offs to consider. Venturi principle explained.
5Type Colors.keys( ) and press Enter.
The dictionary presents a list of the keys it contains. You can use these keys to automate access to the dictionary.
6Type the following code (pressing Enter after each line and pressing Enter twice after the last line):
The example code outputs a listing of each of the user names and the user’s favorite color. Using dictionaries can make creating useful output a lot easier. The use of a meaningful key means that the key can easily be part of the output.
7Type Colors[“Sarah”] = “Purple” and press Enter.
The dictionary content is updated so that Sarah now likes Purple instead of Yellow.
8Type Colors.update({“Harry”: “Orange”}) and press Enter.
A new entry is added to the dictionary.
9Place your cursor at the end of the third line of the code you typed in Step 6 and press Enter.
The editor creates a copy of the code for you. This is a time-saving technique that you can use in the Python Shell when you experiment while using code that takes a while to type. Even though you have to type it the first time, you have no good reason to type it the second time.
10Press Enter twice.
Notice that Harry is added in sorted order. In addition, Sarah’s entry is changed to the color Purple.
11Type del Colors[“Sam”] and press Enter.
Python removes Sam’s entry from the dictionary.
12Repeat Steps 9 and 10.
You verify that Sam’s entry is actually gone.
13Type len(Colors) and press Enter.
The output value of 3 verifies that the dictionary contains only three entries now, rather than 4.
14Type Colors.clear( ) and press Enter. Then, Type len(Colors) and press Enter.
Python reports that Colors has 0 entries, so the dictionary is now empty.
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Active1 month ago
$begingroup$I would like to get a deeply-nested value, for example
{'a':{'b':{'c':'myValue'}}
by providing the keys to traverse. I tried chaining together .get() but that didn't work for cases where some of the keys were missing—in those cases, I want to get None
instead.Could this solution be improved?
Martin BurchMartin Burch
$endgroup$4 Answers
$begingroup$Unless I'm missing something you'd like to implement, I would go for a simple loop instead of using recursion:
ChatterOneChatterOne
$endgroup$$begingroup$If you were to solve it with a third-party package, like
jsonpath-rw
, the solution would be as simple as constructing the path by joining the keys with a dot and parsing the dictionary:Some code style notes about your current approach:
- Python functions does not follow the camel case naming conventions, put an underscore between words -
nested_get()
instead ofnestedGet()
- there should be extra spaces after the commas (PEP8 reference)
- improve on variable naming, make them more descriptive - for instance,
p
can be named aspath
- use
print()
function instead of a statement for Python3.x compatibility
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$endgroup$Python Create Dictionary From List Of Variables In Research Science
$begingroup$You can chain together
dict.get()
functions and use the optional default
argument and specify an empty dict to return instead of None
if the key doesn't exist. Except, let the last .get()
return None
if the key is not found.If any of the keys to be traversed are missing, a empty dict is returned and the following
.get()
s in the chain will be called on the empty dict, which is fine., The final .get()
in the chain will either return the value if all the keys exist or will return None
as desired.example 1:
example 2:
Adam PoradAdam Porad
$endgroup$$begingroup$I like the following approach that makes use of
functools.reduce
. It generalizes nicely to other indexable sequences such as lists and tuples.Create Dictionary From List Of Tuples
This can be further simplified by direct access to the
__getitem__
method of the sequences, which leads to a noticeable increase in performance (I measured 20-35% for different test data):Usage:
If one prefers soft failure for missing keys/indices, one can catch
KeyError
or IndexError
.normaniusnormanius
$endgroup$