用方括号括起来时，foreach 循环之前的变量是什么意思（PySpark）

Question

I am still at the initial phases of learning pyspark, and I found below code confusing. Can someone, please explain this to me

     Code  :    
    zipsSchema = smartphoneDF.schema
    print(type(zipsSchema))
    [**field** for field in zipsSchema]

  What does "field" before "for"  mean, and why is the entire statement enclosed in "[]" When I try to write the same 

    My code is as follows :

 zipsSchema = smartphoneDF.schema
    print(type(zipsSchema))
   for field in zipsSchema 
     print(field)

Answer 1

field is an element from the zipsSchema struct type.

Rather than creating empty list and addint elements to the list we can write for loop in single line using [field for field in zipsSchema] is list comprehension in python.

Example:

smartphoneDF=spark.createDataFrame([("1","a")],["id","name"])

zipsSchema=smartphoneDF.schema

fields_lc=[field for field in zipsSchema]
#[StructField(id,StringType,true), StructField(name,StringType,true)]

fields_fl=[]

for field in zipsSchema:
    fields_fl.append(field)

fields_fl
#[StructField(id,StringType,true), StructField(name,StringType,true)]

As you can see fields_lc , fields_fl values are same and creation is different.