lambda arguments: expression     

# a is an argument and a+10 is an expression which got evaluated and returned.  
x = lambda a:a+10 
# Here we are printing the function object
print(x)
print("sum = ",x(20))

 at 0x0000019E285D16A8>
sum =  30

def x(a):
    return a+10
print(sum = x(10))

# a and b are the arguments and a*b is the expression which gets evaluated and returned.  
x = lambda a,b: a*b
print("mul = ", x(20,10))
Output:
mul =  200

Why use lambda function?
The main role of the lambda function is better described in the scenarios when we use them anonymously inside another function. In Python, the lambda function can be used as an argument to the higher-order functions which accepts other functions as arguments.
Consider the following example:
Example 1:
#the function table(n) prints the table of n  
def table(n):  
    return lambda a:a*n # a will contain the iteration variable i and a multiple of n is returned at each function call  
n = int(input("Enter the number:"))  
b = table(n) #the entered number is passed into the function table. b will contain a lambda function which is called again and again with the iteration variable i  
for i in range(1,11):  
    print(n,"X",i,"=",b(i)) #the lambda function b is called with the iteration variable i
</span></code></pre>
</div>
<p>输出：</p>
<div class="hcb_wrap">
<pre class="prism line-numbers lang-python" data-lang="Java"><code><span span="" style="font-size: 10pt;">Enter the number:10
10 X 1 = 10 
10 X 2 = 20
10 X 3 = 30
10 X 4 = 40
10 X 5 = 50
10 X 6 = 60
10 X 7 = 70
10 X 8 = 80
10 X 9 = 90
10 X 10 = 100
</span></code></pre>
</div>
<p>lambda函数通常与Python内置函数filter()函数和map()函数。</p>
<h4>将lambda函数与filter()一起使用</h4>
<p>Python内置的filter()函数接受一个函数和一个列表作为参数。它提供了一种过滤掉序列中所有元素的有效方法。它返回新的序列，其中函数求值为True。</p>
<p>考虑以下示例，其中我们从给定列表中过滤出唯一的奇数。</p>
<div class="hcb_wrap">
<pre class="prism line-numbers lang-python" data-lang="Java"><code><span span="" style="font-size: 10pt;">#program to filter out the tuple which contains odd numbers  
lst = (10,22,37,41,100,123,29)
oddlist = tuple(filter(lambda x:(x%3 == 0),lst)) # the tuple contains all the items of the tuple for which the lambda function evaluates to true  
print(oddlist)  
</span></code></pre>
</div>
<p>输出：</p>
<div class="hcb_wrap">
<pre class="prism line-numbers lang-python" data-lang="Java"><code><span span="" style="font-size: 10pt;">(37, 41, 123, 29)
</span></code></pre>
</div>
<h4>将lambda函数与map()一起使用</h4>
<p>Python的map()函数接受一个函数和一个列表。它提供了一个新列表，其中包含该函数为每个项目返回的所有已修改项目。</p>
<p>考虑下面的map()函数示例。</p>
<div class="hcb_wrap">
<pre class="prism line-numbers lang-python" data-lang="Java"><code><span span="" style="font-size: 10pt;">#program to filter out the list which contains odd numbers  
lst = (10,20,30,40,50,60)
square_list = list(map(lambda x:x**2,lst)) # the tuple contains all the items of the list for which the lambda function evaluates to true  
print(square_tuple)  
</span></code></pre>
</div>
<p>输出：</p>
<div class="hcb_wrap">
<pre class="prism line-numbers lang-python" data-lang="Java"><code><span span="" style="font-size: 10pt;">(100, 400, 900, 1600, 2500, 3600)
</span></code></pre>
</div>

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