Difference between builder expression and list resolution

Seven, generator expression and list resolution differences Builder expression:

Format: (expr for ITER in iterable [if condition])

The generator is the result of an iteration, not an expression evaluated immediately

Gets a generator object, not a list

Cannot use index, append, etc. list operations

can be converted to list object using the list () factory method

difference between builder and column expressions :

The outermost layer of the builder format is one (), while the outermost list parsing format is a []

The generator is to not read the data once, and the list resolution is to read all the data (memory-consuming)

The generator Returns a generator object (not directly looping), and list resolution returns a new list

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#引入时间工具

Import time

f = open ("E:/pythondata/ods_hbv_addattention")

Start1=time.clock ()

Lines1 = [T.split ("") for T in F]

End1=time.clock ()

Print End1-start1

Print type (lines1)

#文件越大体现越明显

Start2 = Time.clock ()

Lines2 = (T.split (",") for T in F)

End2 = Time.clock ()

Print End2-start2

Print type (lines2)

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