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Introduce four python functions that are commonly used by great gods but not commonly used by you

Https://mp.weixin.qq.com/s/C2nw4JShmj1FlLeDy0IeRA

Today, we will talk about four functions: assert, map,filter,reduce.

Assert

Commonly known as assertion! That is to say, to assert a thing, if it is true, the program will continue; if it is false, an error will be reported.

How to use it?

Two uses

Assert

Assert

First kind

Def avg (marks):

Assert len (marks)! =

Return sum (marks) / len (marks)

Mark1 = []

Print ("Average of mark1:", avg (mark1))

The result is

AssertionError

The second kind

Def avg (marks):

Assert len (marks)! =, "List is empty."

Return sum (marks) / len (marks)

Mark2 = [55, 88, 78, 90, 79]

Print ("Average of mark2:", avg (mark2))

Mark1 = []

Print ("Average of mark1:", avg (mark1))

The result is

Average of mark2: 78.0

AssertionError: List is empty.

Map

In many cases, we perform the same operation on the data in a list, such as:

Items = [1,2,3,4,5]

Squared = []

For i in item s:

Squared. Append (iTunes * 2)

At this point, you can use map operation in the format:

Map (function_to_apply, list_input)

The specific operation is

Items = [1,2,3,4,5]

Squared = list (map (lambda x: Xerox * 2, items))

Of course, functions can be put in list.

Def multiply (x):

Return (xonomx)

Def add (x):

Return (xonomx)

Funcs = [multiply, add]

For i in range (5):

Value = list (map (lambda x: X (I), funcs))

Print (value)

# Output:

# [0, 0]

# [1, 2]

# [4, 4]

# [9, 6]

# [16, 8]

Of course, you can also perform str2id operations.

A = ['5','2','3','4','5']

Print (list (map (int, a)

# [5, 2, 3, 4, 5]

Filter

The filter function is to filter and filter a given condition.

Number_list = range (- 5,5)

Less_than_zero = list (filter (lambda x: X)

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