Powerful zip

1. Code guide

First look at this code:

>>> name=('jack','beginman','sony','pcky')
>>> age=(2001,2003,2005,2000)
>>> for a,n in zip(name,age):
    print a,n

Output:

jack 2001

beginman 2003

sony 2005

pcky 2000

Look at this piece of code again:

all={"jack":2001,"beginman":2003,"sony":2005,"pcky":2000}
 for i in all.keys():
     print i,all[i]

Output:

sony 2005

pcky 2000

jack 2001

beginman 2003

Find the difference between them?

The most obvious one is: the first one is simple, flexible, and can be input sequentially.

2. zip() function

It is a built-in function of Python, (built-in functions related to sequences are: sorted(), reversed(), enumerate(), zip()), among which sorted() and zip() returns a sequence (list) object, reversed(), enumerate() returns an iterator (similar to a sequence)

>>> type(sorted(s))
 <type &#39;list&#39;>
 >>> type(zip(s))
 <type &#39;list&#39;>
 >>> type(reversed(s))
 <type &#39;listreverseiterator&#39;>
 >>> type(enumerate(s))
 <type &#39;enumerate&#39;>

So what is the zip() function?

Let’s help(zip) take a look:

>>> help(zip)

Help on built-in function zip in module __builtin__:

zip(...)

zip( seq1 [, seq2 [...]]) -> [(seq1[0], seq2[0] ...), (...)]

Return a list of tuples, where each tuple contains the i-th element

from each of the argument sequences. The returned list is truncated

in length to the length of the shortest argument sequence. [seql, ...]) accepts a series of iterable objects as parameters, packs the corresponding elements in the objects into tuples, and then returns a list composed of these tuples. If the lengths of the parameters passed in are not equal, the length of the returned list will be the same as the object with the shortest length among the parameters.

>>> z1=[1,2,3]
 >>> z2=[4,5,6]
 >>> result=zip(z1,z2)
 >>> result
 [(1, 4), (2, 5), (3, 6)]
 >>> z3=[4,5,6,7]
 >>> result=zip(z1,z3)
 >>> result
 [(1, 4), (2, 5), (3, 6)]
 >>>

zip() is used with the * operator to decompress the zipped list object

>>> zip(*result)

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

A closer understanding:

* Two-dimensional matrix transformation (row and column exchange of matrix)

For example, we have a two-dimensional matrix described by a list

a = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

We can also easily complete this task through python list derivation

print [ [row[col] for row in a] for col in range(len(a[0]))]

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

Another confusing method Just use the zip function:

>>> a = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

>>> zip(*a)

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

>>> map(list,zip(*a))

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

zip function accepts any number of sequences as parameters, and combines all sequences into one element according to the same index. The tuple formed by merging each sequence New sequence, the length of the new sequence shall be based on the shortest sequence in the parameters. In addition, the (*) operator combined with the zip function can achieve the opposite function of zip, that is, split the merged sequence into multiple tuples.

①New sequence of tuples

>>>>x=[1,2,3],y=['a','b','c']

>>>>zip(x,y)

[(1,'a'),(2,'b'),(3,'c')]

②The length of the new sequence is based on the shortest sequence among the parameters.

>>> >x=[1,2],y=['a','b','c']

>>>zip(x,y)

[(1,'a'),(2,' b')]

③(*) operator combined with the zip function can achieve the opposite function of zip, that is, split the merged sequence into multiple tuples.

>>>>x=[1,2,3],y=['a','b','c']

>>>>zip(*zip(x,y))

[ (1,2,3),('a','b','c')]