Python lambda function printing <function <lambda> at 0x7fcbbc740668> instead of value

14,510

Solution 1

You aren't calling the function. It's the same as if you wrote print convert_ascii instead of print convert_ascii(i).

Try

print (lambda x: chr(ord(x) + 1))(i)

Note that I changed ord(i) to ord(x) in the function body.

Solution 2

The Lambda Keyword returns an anonymous function:

>>> func = lambda x: x+1
>>> print(func)
<function <lambda> at 0x7f0310160668>

the above is (not counting the behind-the-scenes magic) equivalent to:

>>> def func(x):
        return x+1

>>> print(func)
<function func at 0x7fa73d3e6bf8>

to invoke the function, lambda or not, you still have to call it:

>>> print(func)
<function <lambda> at 0x7f0310160668>
>>> func(123)
124

That said, Lambdas are not very well suited to this situation, and are better used if a function or construct requires a short function.

>>> word = "spam"
>>> map(lambda x: chr(ord(x) + 1), word)

Solution 3

Currently you are printing a function object. You have to call the function.

Receive the function in a variable and call it with a parameter.

for i in word:
  print convert_ascii(i)
  fun=lambda x: chr(ord(x) + 1)
  print fun(some_arg) 

Solution 4

You are trying to print the function itself. Instead of that, assign the function in a variable, and pass the parameter to the variable, or use the same within print itself.

for i in word:
  z = lambda x: chr(ord(x) + 1)
  print z(i)

or

for i in word:
  print (lambda x: chr(ord(x) + 1))(i)

or to learn map, you can use map to get the same result

for i in word:
  print "".join(map(lambda x: chr(ord(x) + 1), i))
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pkill
Author by

pkill

Updated on June 09, 2022

Comments

  • pkill
    pkill over 1 year

    I am a beginner in python, and I was playing around with lambda functions. I was writing a program using lambda function to print characters that are +1 the ascii value of the input characters. My code is

    #!/usr/bin/python
    import sys
    try:
      word = sys.argv[1]
    except:
      print "No arguments passed"
      sys.exit(1)
    
    def convert_ascii(char):
      return  "".join(chr(ord(char) + 1))
    
    for i in word:
      print convert_ascii(i)
      print lambda x: chr(ord(i) + 1)
    

    I have a function convert_ascii that does the same thing as lambda. However, my output is

    /usr/bin/python2.7 /home/user1/PycharmProjects/test/Tut1/asciipl2.py "abc def ghi"
    b
    <function <lambda> at 0x7f0310160668>
    c
    <function <lambda> at 0x7f0310160668>
    d
    <function <lambda> at 0x7f0310160668>
    !
    <function <lambda> at 0x7f0310160668>
    e
    <function <lambda> at 0x7f0310160668>
    f
    <function <lambda> at 0x7f0310160668>
    g
    <function <lambda> at 0x7f0310160668>
    !
    <function <lambda> at 0x7f0310160668>
    h
    <function <lambda> at 0x7f0310160668>
    i
    <function <lambda> at 0x7f0310160668>
    j
    <function <lambda> at 0x7f0310160668>
    

    The purpose of this script is learning lambda, though there are other ways to do this program. Please let me know what am I doing wrong. Process finished with exit code 0

  • Vasily Ryabov
    Vasily Ryabov about 8 years
    Correct. But saving lambda to a variable looks like creating a named function that is vice versa to lambda idea. For example, QuantifiedCode.com service treats it as an anti-pattern raising a warning.
  • chepner
    chepner about 8 years
    You don't need to assign the function to a variable; print (lambda x: chr(ord(x) + 1))(i) works the same.
  • pkill
    pkill about 8 years
    Never knew that. Thanks
  • chepner
    chepner about 8 years
    List comprehensions are more efficient than mapping a user-defined function over a list: [ chr(ord(x) + 1) for x in word].
  • saulspatz
    saulspatz about 8 years
    A lambda is a literal function. It doesn't have to be anonymous. One might equally well say that giving a name to a literal string or a literal number is an "anti-pattern".
  • Ahsanul Haque
    Ahsanul Haque about 8 years
    I know, it's basiclly matter of calling the function.
  • chepner
    chepner about 8 years
    Lambdas are intended for situations where you can't or don't need to assign a name. If you're going to write foo = lambda x: ..., you may as well write def foo(x): .... I can't think of a situation where you would use a lambda expression with a list comprehension.
  • Azsgy
    Azsgy about 8 years
    Although fo note that in this case the Lambda is useless. The code in this answer is equivalent to print(chr(ord(x) + 1))
  • Ahsanul Haque
    Ahsanul Haque about 8 years
    [(lambda x: x*x)(x) for x in range(10)] can't you write that?
  • chepner
    chepner about 8 years
    The OP's stated purpose is to learn how lambda expressions work. Where it is appropriate to use them is off-topic for this particular question.
  • chepner
    chepner about 8 years
    You could, but why would you? [x*x for x in range(10)]
  • Azsgy
    Azsgy about 8 years
    @chepner, yeah, just caught that. Will change to OP's example. Yes, list comprehensions would be better.
  • nohup
    nohup about 8 years
    Thanks chepner. I copy-pasted, and hence I didn't notice. Changed.
  • pkill
    pkill about 8 years
    Though I used i instead of x in lambda functions, the result was the same. In lambda, I accepted the var as x, but iterated as i, and still it worked. Any idea why?
  • chepner
    chepner about 8 years
    Since the lambda expression is defined and called in the same scope, the i as a free variable in the expression is bound to the same value as x once the expression is called. It's technically a bug, but under the circumstances works the same as the correctly written code.
  • pkill
    pkill about 8 years
    Thanks @chepner. This really helped.
  • saulspatz
    saulspatz about 8 years
    @chepner You're right, but I think the OP is just trying to figure out how lambdas work in python, don't you?
  • chepner
    chepner about 8 years
    I do, but you're the one who brought up using a lambda expression in a list comprehension.
  • saulspatz
    saulspatz about 8 years
    @chepner. I think you're confusing me with Ahsanul Hasque. I didn't say anything about list comprehensions. I may have scrolled down too fast. I thought you were talking about the OP's code, not Ahsanul's.