Python Basics: Zip and dict detailed

A. zip function: Accepts any number of sequences (including 0 and 1) as parameters, returning a tuple list.

1. Example 1:

x = [1, 2, 3]y = [4, 5, 6]z = [7, 8, 9]xyz = Zip (x, y, z) print xyz

The result of the operation is:

[(1, 4, 7), (2, 5, 8), (3, 6, 9)]

From this result, we can see the basic operation of the ZIP function.

2. Example 2:

x = [1, 2, 3]y = [4, 5, 6, 7]xy = Zip (x, y) print xy

The result of the operation is:

[(1, 4), (2, 5), (3, 6)]

From this result, we can see how the length of the zip function is handled.

3. Example 3:

x = [1, 2, 3]x = Zip (x) print X

The result of the operation is:

[(1,), (2,), (3,)]

From this result you can see how the ZIP function works when there is only one parameter.

4. Example 4:

x = Zip () print X

The result of the operation is:

[]

From this result, you can see how the zip function works without parameters.

5. Example 5:

x = [1, 2, 3]y = [4, 5, 6]z = [7, 8, 9]xyz = Zip (x, y, z) u = Zip (*xyz) print U

The result of the operation is:

[(1, 2, 3), (4, 5, 6), (7, 8, 9)]

It is generally thought that this is a unzip process, and its operating mechanism is this:

Before running Zip (*xyz), the value of XYZ is: [(1, 4, 7), (2, 5, 8), (3, 6, 9)]

Then, Zip (*xyz) is equivalent to zip ((1, 4, 7), (2, 5, 8), (3, 6, 9))

So the result is: [(1, 2, 3), (4, 5, 6), (7, 8, 9)]

Note: Using *list/tuple in a function call means separating the list/tuple, passing it as a positional parameter to the corresponding function (provided that the corresponding function supports an indefinite number of positional parameters)

6. Example 6:

x = [1, 2, 3]r = Zip (* [x] * 3) Print R

The result of the operation is:

[(1, 1, 1), (2, 2, 2), (3, 3, 3)]

It operates in such a way that:

[x] generates a list of lists that have only one element x

[x] * 3 generates a list of lists, it has 3 elements, [x, X, X]

The meaning of Zip (* [x] * 3) is clear, zip (x, x, x)

Second, dict operation

1. Create a dictionary using zip

Key = ' ABCDE '

Value = Range (1, 6)

Dict (Zip (key, value))

2. Use items () to traverse the dictionary

For Key,value in D.items ():

3. use GET, pop to get/delete key

First, Dict[key] and delete Dict[key] can also get/delete key. However, a keyerror exception is thrown when key does not exist. To avoid throwing exceptions, you can use the Get and pop functions with the Defaut parameter

• Get (key[, default])
  If key is in the dictionary, the corresponding value is returned, otherwise the default is returned. So it never throws an exception.
• Pop (key[, default])
  If default is not set, deleting key will throw an exception if key is not in the dictionary. Add default when used.

4, Dict (Dict1, **dict2) Merge two dictionaries

Merging two dictionaries you can divide two dictionaries into key-value pairs, connect two key-value pairs, and create a new dictionary. That is dict(dict1.items()+dict2.items()) , but the efficiency is somewhat low.
Use a more efficient dict(dict1, **dict2) connection to two dictionaries.

in []: dict1out[29]: {' A ':1,' B ':2,' C ':3}in [(): dict2out[30]: { ' d ': 4,  ' E ': 5,  ' F ': 6} In [31]: dict (dict1, **dict2) Out[31]: { ' a ': 1,  ' B ': Span class= "DV" >2,  ' C ': 3,  ' d ': 4,  ' E ': 5,  ' F ': 6}         

-m timeit -s ‘dict1=dict2=dict(a=1,b=2)‘ ‘dict3=dict(dict1,**dict2)‘1000000 loops, best of 3: 0.573 usec per loop$ python -m timeit -s ‘dict1=dict2=dict(a=1,b=2)‘ ‘dict3=dict(dict1.items()+dict2.items())‘100000 loops, best of 3: 2.21 usec per loop

5. Use keys () and values () to get the keyword and value

D.keys ()

D.values ()

6, update the dictionary using update (), the same as 4 dict (Dict1, **dict2) effect

1Dict1 = {"a":"Apple","b":"Banana"}2 Print(Dict1)3Dict2 = {"C":"Grape","D":"Orange"}4 dict1.update (DICT2)5 Print(Dict1)

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Output:

{' A ': ' Apple ', ' B ': ' Banana '}
{' C ': ' Grape ', ' a ': ' Apple ', ' B ': ' Banana ', ' d ': ' Orange '}

7. Sorting using sorted

#按照key排序
Print (sorted (Dict1.items (), Key=lambda d:d[0]))
#按照value排序
Print (sorted (Dict1.items (), Key=lambda d:d[1]))

8. Use SetDefault to set default values

Dict = {}
Dict.setdefault ("a")

9. Pop () and clear () delete

1d={"a": 1,"b": 2,"C": 3}2 Print(d)3 #Output4 #{"A": 1, "B": 2, "C": 3}5 6D1=d.pop ("a")#d1=17 Print(d)8 #Output9 #{"B": 2, "C": 3}Ten  OneD2=d.pop ("F", 100)#d2=100 A Print(d) - #Output - #{"B": 2, "C": 3}

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D.clear () #将字典d清空

Print (d) #输出 {}

10. Use the Fromkeys () function to create a new dictionary, which is the key for the dictionary of elements in the sequence SEQ, and value is the initial value corresponding to all keys in the dictionary.

1 seq={'name','age','score  '}2 d=dict.fromkeys (seq,100)3print(d) 4 # Output 5 # {' name ': +, ' age ': +, ' score ':

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11. Use Popitems () to randomly return and delete a pair of keys and values (items) in the dictionary

1seq={'name',' Age','score'}2D=dict.fromkeys (seq,100)3 Print(d)#output: {' age ': +, ' name ': +, ' score ':4D2=D.popitem ()5 Print(D2)#output: (' age ', +)6 Print(d)#output: {' name ': +, ' score ':

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Python Basics: Zip and dict detailed