Python check if list of keys exist in dictionary

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I have a dictionary that looks like that:

grades = {
        'alex' : 11,
        'bob'  : 10,
        'john' : 14,
        'peter': 7
       }

and a list of names students = ('alex', 'john')

I need to check that all the names in students exist as keys in grades dict.

grades can have more names, but all the names in students should be in grades

There must be a straightforward way to do it, but i'm still new to python and can't figure it out. tried if students in grades, didn't work.

In the actual cases, the lists will be much bigger.

Use all():

if all(name in grades for name in students):
    # whatever

Check if any of the list of keys are present in a dictionary, Check if items in a list exist in dictionary (1 answer). Closed 4 years ago. You could use any and iterate over each key you want to check if any(key in dict for key in ['asdf', 'qwer', 'zxcf']): # contains at least one of them. This will short-circuit you could try using list comprehension in python: if any([True for  Dictionary provides a method get () that accepts a key and default value. Python. dict.get (key [, default]) 1. dict.get(key[, default]) If given key exists in dictionary then it returns its value, If given key does not exists in dictionary then it returns the passed default value argument.

>>> grades = {
        'alex' : 11,
        'bob'  : 10,
        'john' : 14,
        'peter': 7
}
>>> names = ('alex', 'john')
>>> set(names).issubset(grades)
True
>>> names = ('ben', 'tom')
>>> set(names).issubset(grades)
False

Calling it class is invalid so I changed it to names.

Python, Python | Get dictionary keys as a list. raghvendra3499. Check out this Author's contributed articles. If you like GeeksforGeeks and would like  The dictionary contains the elements with key and its associated value. Check If Key Exists In Dictionary With For Loop in Python. You can find the given key if it exists in the given Dictionary. To perform this task, you have to use the for loop with if condition inside. The if condition finds the matching key if present in the given dictionary. The given key is stored in the variable ‘mykey’.

Assuming students as set

if not (students - grades.keys()):
    print("All keys exist")

If not convert it to set

if not (set(students) - grades.keys()):
    print("All keys exist")

Python : How to check if a key exists in dictionary ? – thispointer.com, Different ways to Remove a key from Dictionary in Python | del vs dict.pop() · python : How to create a list of all the keys in the Dictionary ? Python:  Another method is has_key () (if still using Python 2.X): If you want to retrieve a default value when the key does not exist, use value = a.get (key, default_value) . If you want to set the default value at the same time in case the key does not exist, use value = a.setdefault (key, default_value).

Python : How to check if any element of a list is a key in dictionary, Here, we simply iterate through each element in the list. In each iteration, we check if the element exists as a key in the dictionary (line 2). A common use for checking the existence of a key in a dictionary before mutating it is to default-initialize the value (e.g. if your values are lists, for example, and you want to ensure that there is an empty list to which you can append when inserting the first value for a key).

how to check if key exists in dictionary python Code Example, Get code examples like "how to check if key exists in dictionary python" instantly right from your google search results with the Grepper Chrome  Function except to be called like: keys_exists(dict_element_to_test, 'key_level_0', 'key_level_1', 'key_level_n', ..). At least two arguments are required, the element and one key, but you can add how many keys you want.

Using key in list to check if key is contained in list, If possible, you should change the list to a set or dictionary instead, because defines a list l and then calls if 3 in l to check if the number 3 exists in the list. In python 3 you can say set(("foo","bar")) <= myDict.keys() which avoids the temporary set, so is much faster. For my testing it is about the same speed as using all when the query was 10 items. For my testing it is about the same speed as using all when the query was 10 items.

Comments
  • Possible duplicate of How do I check that multiple keys are in a dict in a single pass?
  • @SvenMarnach: If I could up vote your comment more than once, I would.
  • Great! Any shortcut way to get the elements that are missing from the dic if the condition is False?
  • @guival Yup, you can use set operations, e.g. set(students) - grades.keys() in Python 3.
  • is there a way to check if any of a list of keys is a sub string in a string?
  • @Jonathan Not sure what you mean, maybe any(k in my_string for k in keys)?
  • This can't short-cut, in contrast to all(). It will always be O(m+n), where m and n are the respective sizes of names and grades. Using all() will be O(m), and might short-cut.
  • @SvenMarnach Right, I'll just leave it here since it is another approach but I agree that yours is the best.
  • Definitely leave it here! It's an interesting approach in any case.