get
- default value of a non existing key while accessing¶Especially handy if you're unsure about the presence of a key.
my_dict = {'a': 1, 'b': 2, 'c': 3}
Don't do it like this.
if 'g' in my_dict:
value = my_dict['g']
else:
value = 'some default value'
print(value)
Or like this.
try:
value = my_dict['g']
except KeyError:
value = 'some default value'
print(value)
value = my_dict.get('g', 'some default value')
print(value)
Note that if you don't provide the default value for get
, the return value will be None
if the key is not present in the dictionary
value = my_dict.get('g')
print(value is None)
setdefault
- same as get
but also sets the value if not present¶Don't do it like this.
my_dict = {'a': 1, 'b': 2, 'c': 3}
key = 'g'
if key in my_dict:
value = my_dict[key]
else:
value = 'some default value'
my_dict[key] = value
print(value)
print(my_dict)
my_dict = {'a': 1, 'b': 2, 'c': 3}
key = 'g'
value = my_dict.setdefault(key, 'some default value')
print(value)
print(my_dict)
Let's say we have a collection of numbers and we want to store those as a dictionary where the number is key and it's square is the value.
numbers = (1, 5, 10)
Don't do it like this.
squares = {}
for num in numbers:
squares[num] = num**2
print(squares)
squares = {num: num**2 for num in numbers}
print(squares)
keys = ('a', 'b', 'c')
values = [True, 100, 'John Doe']
Don't do it like this.
my_dict = {}
for idx, key in enumerate(keys):
my_dict[key] = values[idx]
print(my_dict)
my_dict = {k: v for k, v in zip(keys, values)}
print(my_dict)
# Or even like this:
my_dict2 = dict(zip(keys, values))
assert my_dict2 == my_dict
my_dict = {'age': 83, 'is gangster': True, 'name': 'John Doe'}
Don't do it like this.
for key in my_dict:
val = my_dict[key]
print('key: {:15s} value: {}'.format(key, val))
for key, val in my_dict.items():
print('key: {:15s} value: {}'.format(key, val))