Python has two primitive loop commands:
With the while loop we can execute a set of statements as long as a condition is true.
Print i as long as i is less than 6:
i = 1 while i < 6: print(i) i += 1
Note: remember to increment i, or else the loop will continue forever.
Python supports the usual logical conditions from mathematics:
These conditions can be used in several ways, most commonly in “if statements” and loops.
An “if statement” is written by using the if keyword. Continue reading Python If … Else
Python has a set of built-in methods that you can use on dictionaries.
| Method | Description |
|---|---|
| clear() | Removes all the elements from the dictionary |
| copy() | Returns a copy of the dictionary |
| fromkeys() | Returns a dictionary with the specified keys and value |
| get() | Returns the value of the specified key |
| items() | Returns a list containing a tuple for each key value pair |
| keys() | Returns a list containing the dictionary’s keys |
| pop() | Removes the element with the specified key |
| popitem() | Removes the last inserted key-value pair |
| setdefault() | Returns the value of the specified key. If the key does not exist: insert the key, with the specified value |
| update() | Updates the dictionary with the specified key-value pairs |
| values() | Returns a list of all the values in the dictionary |
A dictionary can contain dictionaries, this is called nested dictionaries.
Create a dictionary that contain three dictionaries:
myfamily = {
"child1" : {
"name" : "Emil",
"year" : 2004
},
"child2" : {
"name" : "Tobias",
"year" : 2007
},
"child3" : {
"name" : "Linus",
"year" : 2011
}
}
Or, if you want to add three dictionaries into a new dictionary: Continue reading Python – Nested Dictionaries
You cannot copy a dictionary simply by typing dict2 =, because:
dict1dict2 will only be a reference to dict1, and changes made in dict1 will automatically also be made in dict2.
There are ways to make a copy, one way is to use the built-in Dictionary method
copy()
Make a copy of a dictionary with the copy() method:
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
mydict = thisdict.copy()
print(mydict)
Another way to make a copy is to use the built-in function dict(). Continue reading Python – Copy Dictionaries
You can loop through a dictionary by using a for loop.
When looping through a dictionary, the return value are the keys of the dictionary, but there are methods to return the values as well.
Print all key names in the dictionary, one by one:
for x in thisdict:
print(x)
There are several methods to remove items from a dictionary:
The pop() method removes the item with the specified key name:
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
thisdict.pop("model")
print(thisdict)
Adding an item to the dictionary is done by using a new index key and assigning a value to it:
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
thisdict["color"] = "red"
print(thisdict)
You can change the value of a specific item by referring to its key name:
Change the “year” to 2018:
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
thisdict["year"] = 2018
You can access the items of a dictionary by referring to its key name, inside square brackets:
Get the value of the “model” key:
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
x = thisdict["model"]
There is also a method called get() that will give you the same result: Continue reading Python – Access Dictionary Items