4-4 how multiple small strings together into one big string

Original link: http://www.cnblogs.com/smulngy/p/8871854.html

1, using the operator " + "

>>> s1 = 'abcdefg'
>>> s2 = '12345'
>>> s1 + s2
'abcdefg12345'

This "+" is overloaded operator actually calls str .__ add__ built-in method.

>>> str.__add__ (s1,s2)
'abcdefg12345'

When this method when large volumes of data, will take up more resources.

If only a very simple string concatenation can be used, which is more simple.

2, using str.join ()

>>> help(str.join)
Help on method_descriptor:

join(...)
    S.join(iterable) -> string
    
    Return a string which is the concatenation of the strings in the
iterable.  The separator between elements is S.

help(str.join)

Passing an iterator object is used as a delimiter strings S connected objects.

Example:

>>> ';'.join(['abc','123',456,'xyz'])

Traceback (most recent call last):
  File "<pyshell#46>", line 1, in <module>
    ';'.join(['abc','123',456,'xyz'])
TypeError: sequence item 2: expected string, int found


>>> ';'.join(['abc','123','456','xyz'])
'abc;123;456;xyz'
>>> ';'.join(['abc','123','456','xyz'])
'abc;123;456;xyz'
>>> ''.join(['abc','123','456','xyz'])
'abc123456xyz'
>>> ' '.join(['abc','123','456','xyz'])
'abc 123 456 xyz'

Take the above example list is non-string, a string of splicing, there are two methods

Method One: list comprehensions

>>> ''.join([str(x) for x in ['abc','123',456,'xyz']])
'abc123456xyz'

Each item in the list by str (x) into a string.

By means of a list of analytical formula will generate a temporary list, if the list is long, it will result in larger waste. Not recommended for use.

Method two: generator expression

>>> (str(x) for x in['abc','123',456,'xyz'] )
<generator object <genexpr> at 0x02C60B70>

The above list of parsed block number "[]" to parentheses "()" becomes the object generator. When the generator object for each execution, it generates a, unlike the list of one-time parsing all listed, so more to save resources. Recommended .

>>> ''.join(str(x) for x in ['abc','123',456,'xyz'])
'abc123456xyz'

Generator expressions as parameters can not write parentheses "()"

 

Reproduced in: https: //www.cnblogs.com/smulngy/p/8871854.html