Retrieve first value from list python
Solution 1: No, you don’t need to iterate over the list twice: This can be written in one line using and a generator: Solution 2: You can add a guard to a list comprehension to act as a filter You should also avoid shadowing built in names like Question: I have a dictionary where the values are lists of different lengths like so: I would like to convert it to a list of tuples for upload to a database: The most recent thing I have tried is: This does not work, but I can’t tell why.
Retrieve dict values from a list in Python
I have a dictionary where the values are lists of different lengths like so:
I would like to convert it to a list of tuples for upload to a database:
The most recent thing I have tried is:
lst = [] mydict = for k in mydict.keys(): for i in range(len(mydict[k])): count = 0 while count < i: lst.append((k, mydict[k])) count += 1 This does not work, but I can't tell why. Thanks for any help!
It feels like you're over-complicating it a bit.
It should only require 2 loops:
lst = [] for k, vals in mydict.items(): for value in vals: lst.append((k, value)) The first loop is over the dictionary items, the inner loop is over the values list. For each value in the values list, just append a tuple that holds the key and the value to your resultant list.
And, FWIW, there are lots of other spellings here:
lst = [] for k, vals in mydict.items(): lst.extend((k, value) for value in vals) lst = [(k, value) for k, vals in mydict.items() for value in vals] though I'm not a huge fan of the 1-line version.
As for why your version doesn't work, let's take a look and find out:
lst = [] mydict = for k in mydict.keys(): for i in range(len(mydict[k])): count = 0 while count < i: lst.append((k, mydict[k])) count += 1 The first thing that we see is you have an extra loop. For each key, you'll be hitting some of the values twice when you only want to hit them once. You could fix it by removing the loop over range(len(. )) :
lst = [] mydict = for k in mydict.keys(): count = 0 while count < len(mydict[k]): lst.append((k, mydict[k])) count += 1 But, this is already a more verbose (and, IMHO, confusing) way to write it out than the options I've provided above.
You should avoid for loops in python where possible, its very inefficient. Use list comprehension as the most pythonic way to do this. stack is the name of the dict:
[(i,x) for x in stack[i] for i in stack.keys()] new_list = [] for key, values in mydict.items(): for val in values: new_list.append((key, val)) import itertools d = result = [] for k, v in d.items(): result.extend(zip(itertools.cycle(k), v)) for k, v in d.items(): result.extend(itertools.izip(itertools.cycle(k), v)) itertools.repeat could also be used in place of itertools.cycle.
Python - Get value from dictionary for first key that, Is there a Python dictionary method or simple expression that returns a value for the first key (from a list of possible keys) that exists in a dictionary? Details. Lets say I have a Python dictionary with a number of key-value pairs. The existence of any particular key not guaranteed. d =
Retrieve first key-value pair from a dictionary in Python without using list, iter
In case I have a huge dictionary my_dict with a complex structure.
If I want to see its first key-value pair (to understand whats inside), currently I use:
However, this dublicates all the keys in the memory. It is also inconvienient, because pdb.set_trace() does not execute expressions starting with list . It is possible to use iterator:
However, its inconvenient, because I cannot access n'th element easily.
Is there any other easy way to access key-value pairs of dict_items() ?
In Python 2.7 this expression used to work:
Update Ended up using:
This approach at least overcomes the pdb.set_trace() limitation. It also allows to easily access n'th element and does not require any imports like from itertools import islice .
The reason my_dict.items()[0] worked in Python 2.7 and not in Python 3 is because in Python 2 it returned a list and in Python 3 it returns a dictionary view.
To get the same behavior, you have to wrap it in list() or tuple() .
The most memory efficient way would be to create a tuple of the keys.
keys = tuple(my_dict.keys()) my_dictPython first value from list] However, whenever you change the dictionary, you'd have to update/recreate keys .
Another thing to note is order is not guaranteed before Python 3.7, though once keys is created, it's order is.
Python - Get the first character of the first string in a list?, The simplest way is. mylist [0] [0] # get the first character from the first item in the list. but. mylist [0] [:1] # get up to the first character in the first item in the list. would also work. You want to end after the first character (character zero), not start after the first character (character zero), which is what the code in your
Retrieve value from list python2.7
My list looks like as follows:
I would like to retrieve value1, but only if key1 matches a specific string, i'm not sure if i have to iterate over this twice.
No, you don't need to iterate over the list twice:
value = None for d in list: if d[u"Key"] == u"Key1": value = d[u"Value"] This can be written in one line using next() and a generator:
value = next((d[u"Value"] for d in list if d[u"Key"] == u"Key1"), None) You can add a guard to a list comprehension to act as a filter
[d[u"Value"] for d in list if d[u"Key"] == u"Key1"] You should also avoid shadowing built in names like list
Extract values from a Python list, The outer item is a list, and the inner items are dictionaries. You just need to go one level deeper. for audit_item in audit_items_list: for k, v in audit_item.items (): # iterate over key value pairs. # Or get the entire list of each by doing item.keys () or item.values () Use audit_items_list.items () if you are using …
How to get the First Element of a List in Python
Lists in Python are a powerful way to store and manipulate data. They are a fundamental part of Python programming.
Eventually, you'll need to know how to get the first element of a list.
In this post, we'll learn the two best ways of getting the first element of a list in Python.
Getting the first element of a list
To start, let's create a list.
This is a simple list, with five elements.
In Python, you can access elements of a list by using the index and square brackets.
Simply put the index of the element you want to access. Because we want to get the first element of the list, we can use the index 0 .
Here's how to get the first element of the list:
We use 0 instead of 1 because Python is zero-based meaning that the first element is at index 0 and not 1 .
Alternatively, you can take advantage of Python's slicing syntax.
In Python, you can slice a list by using the colon ( : ) character. By passing in the start and end index, you can get a slice of the list.
We can just slice the rest of the list after the first element:
Conclusion
In this post, we learned how to get the first element of a list in Python using two different methods.
The first method is to use the index and square brackets, and the second method is to use the slicing syntax.
Hopefully, you've found this post helpful. Happy coding!
If you want to learn about web development, founding a start-up, bootstrapping a SaaS, and more, follow me on Twitter! You can also join the conversation over at our official Discord!
Give feedback on this page , tweet at us, or join our Discord !