为什么Laravel 4 gitignore composer.lock(why does Laravel 4 gitignore composer.lock)

 SFrame是不可变的，因此它们实际上不支持项目分配。 你在这里看到差异的原因是因为 
 
sf[1]['test']
 
 实际上并不是指SFrame。 “sf [1]”返回一个字典，其中包含与SFrame列名匹配的键，以及与SFrame第二行匹配的值。 当您为“sf [1] ['test']”分配一个数字时，您正在更改返回的字典中的“test”键的值，因此SFrame“sf”不参与分配。 仅引用“test”列的第二个值并赋值“3”的正确方法是： 
 
sf['test'][1] = 3
 
 哪会返回此错误： 
 
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-5-c52dab41d5dd> in <module>()
----> 1 sf['test'][1] = 3

TypeError: 'SArray' object does not support item assignment

SFrames are immutable, so they don't actually support item assignment. The reason for the difference you see here is because 
 
sf[1]['test']
 
isn't actually referring to the SFrame at all. "sf[1]" returns a dictionary with keys that match to the SFrame's column names, and values that match the second row of the SFrame. When you assign a number to "sf[1]['test']", you are changing the value of the "test" key in the dictionary that was returned, so the SFrame "sf" is not involved in the assignment. The correct way to reference only the second value of the column "test" and assign the value "3" is this:
 
sf['test'][1] = 3
 
which would return this error:
 
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-5-c52dab41d5dd> in <module>()
----> 1 sf['test'][1] = 3

TypeError: 'SArray' object does not support item assignment