Lambda-filter-reduce-apply-map of Python built-in functions

• (1) Lambda

Lambda is a useful syntax in Python that allows you to quickly define a single-line minimum function. Similar to a macro in C, it can be used wherever a function is needed.

The basic syntax is as follows:

函数名 = lambda args1,args2,...,argsn : expression

For example:
Add = Lambda x,y:x + y
Print (ADD)

• (2) Filter

filterfunction is equivalent to a filter, the function prototype is: filter(function,sequence) , for each element in the sequence sequence execution function, where function is a bool function, for example:

= [1,2,3,4,5,6,7,8,9,10=lambda%2==0=filter(fun,sequence)print(seq)

The following code indicates that all the even numbers in the sequence are filtered out.

The filter function prototype is roughly as follows:

deffilter(fun,seq):    = []    forin seq:        if fun(item):            filter_seq.append(item)    return

• (3) Map

The basic form of map is: Map (function,sequence), which functions the function on the sequence sequence and returns a final result sequence. Like what:

= [1,2,3,4,5,6=lambda<<2printmap(fun,seq)

The map's function source code is roughly as follows:

defmap(fun,seq):    = []    forin seq:        mapped_seq.append(fun(item))    return(mapped_seq)

• (4) Reduce

The reduce function is in the form of:

reduce(function,sequence,initVal)

functionRepresents a two-tuple function that represents the sequence sequence to be processed, and initVal represents the initial value of the processing. Like what:

= [1,2,3,4,5,6,7,8,9,10=lambda+ yprint(reduce(fun,seq,0))

Indicates that each element in the sequence SEQ starts with an initial value of 0, so the resulting result is 55

reduceThe source code for the function is roughly as follows:

defreduce=None):    =list(seq)    ifisNone:        = Lseq.pop(0)    else:        = initVal    forin Lseq:        = fun(seq,item)    return res

• (5) Apply

applyis used to indirectly replace a function, such as:

def say(a,b):    print(a,b)apply(say,(234,‘Hello World!‘))

Lambda-filter-reduce-apply-map of Python built-in functions