How to convert string representation of list to a list

Question

I was wondering what the simplest way is to convert a string representation of a list like the following to a list  x       quot A quot   quot B quot   quot C quot     quot  D quot     Even in cases where the user puts spaces in between the commas  and spaces inside of the quotes  I need to handle that as well and convert it to  x     quot A quot    quot B quot    quot C quot    quot D quot     I know I can strip spaces with strip   and split   and check for non-letter characters  But the code was getting very kludgy  Is there a quick function that I m not aware of

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and with pure python - not importing any libraries   x for x in  x split      1  split      0  split      1 -1  if x not in

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The eval is dangerous - you shouldn t execute user input   If you have 2 6 or newer  use ast instead of eval    gt  gt  gt  import ast  gt  gt  gt  ast literal eval    A   B    C     D       A    B    C     D     Once you have that  strip the strings   If you re on an older version of Python  you can get very close to what you want with a simple regular expression    gt  gt  gt  x      A      B    C   D      gt  gt  gt  re findall r   s          s     x    A    B    C    D     This isn t as good as the ast solution  for example it doesn t correctly handle escaped quotes in strings  But it s simple  doesn t involve a dangerous eval  and might be good enough for your purpose if you re on an older Python without ast

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import ast l   ast literal eval     A   B   C      D     l    i strip   for i in l

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You may run into such problem while dealing with scraped data stored as Pandas DataFrame   This solution works like charm if the list of values is present as text    def textToList hashtags       return hashtags strip       replace           replace          split       hashtags       A   B   C      D    hashtags   textToList hashtags   Output    A    B    C    D        No external library required

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Assuming that all your inputs are lists and that the double quotes in the input actually don t matter  this can be done with a simple regexp replace   It is a bit perl-y but works like a charm   Note also that the output is now a list of unicode strings  you didn t specify that you needed that  but it seems to make sense given unicode input   import re x   u    A   B   C      D    junkers   re compile            result   junkers sub     x  split      print result --- gt    u A   u B   u C   u D     The junkers variable contains a compiled regexp  for speed  of all characters we don t want  using   as a character required some backslash trickery  The re sub replaces all these characters with nothing  and we split the resulting string at the commas      Note that this also removes spaces from inside entries u   oh no    ---   u ohno     If this is not what you wanted  the regexp needs to be souped up a bit

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I would like to provide a more intuitive patterning solution with regex   The below function takes as input a stringified list containing arbitrary strings    Stepwise explanation  You remove all whitespacing bracketing and value separators  provided they are not part of the values you want to extract  else make the regex more complex   Then you split the cleaned string on single or double quotes and take the non-empty values  or odd indexed values  whatever the preference     def parse strlist sl   import re clean   re sub         s      sl  splitted   re split          clean  values only    s for s in splitted if s        return values only   testsample     21   foo   6    0     A

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There is a quick solution   x   eval     A   B   C      D       Unwanted whitespaces in the list elements may be removed in this way   x    x strip   for x in eval     A   B   C      D

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If it s only a one dimensional list  this can be done without importing anything    gt  gt  gt  x   u    A   B   C      D     gt  gt  gt  ls   x strip       replace          replace          split       gt  gt  gt  ls   A    B    C    D

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gt  gt  gt  import ast  gt  gt  gt  x       quot A quot   quot B quot   quot C quot     quot  D quot     gt  gt  gt  x   ast literal eval x   gt  gt  gt  x   A    B    C     D    gt  gt  gt  x    n strip   for n in x   gt  gt  gt  x   A    B    C    D    ast literal eval   With ast literal eval you can safely evaluate an expression node or a string containing a Python literal or container display  The string or node provided may only consist of the following Python literal structures  strings  bytes  numbers  tuples  lists  dicts  booleans  and None

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The json module is a better solution whenever there is a stringified list of dictionaries  The json loads your data  function can be used to convert it to a list   gt  gt  gt  import json  gt  gt  gt  x       quot A quot   quot B quot   quot C quot     quot  D quot     gt  gt  gt  json loads x    A    B    C     D    Similarly  gt  gt  gt  x       quot A quot   quot B quot   quot C quot      quot D quot   quot E quot      gt  gt  gt  json loads x    A    B    C     D    E

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If you know that your lists only contain quoted strings  this pyparsing example will give you your list of stripped strings  even preserving the original Unicode-ness     gt  gt  gt  from pyparsing import    gt  gt  gt  x  u    A   B   C      D     gt  gt  gt  LBR RBR   map Suppress        gt  gt  gt  qs   quotedString setParseAction removeQuotes  lambda t  t 0  strip     gt  gt  gt  qsList   LBR   delimitedList qs    RBR  gt  gt  gt  print qsList parseString x  asList    u A   u B   u C   u D     If your lists can have more datatypes  or even contain lists within lists  then you will need a more complete grammar - like this one on the pyparsing wiki  which will handle tuples  lists  ints  floats  and quoted strings   Will work with Python versions back to 2 4

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Inspired from some of the answers above that work with base python packages I compared the performance of a few  using Python 3 7 3    Method 1  ast  import ast list map str strip  ast literal eval u    A   B   C      D           A    B    C    D    import timeit timeit timeit stmt  list map str strip  ast literal eval u     A     B     C        D          setup  import ast   number 100000    1 292875313000195   Method 2  json  import json list map str strip  json loads u    A   B   C      D           A    B    C    D    import timeit timeit timeit stmt  list map str strip  json loads u     A     B     C        D          setup  import json   number 100000    0 27833264000014424   Method 3  no import  list map str strip  u    A   B   C      D    strip       replace          split            A    B    C    D    import timeit timeit timeit stmt  list map str strip  u     A     B     C        D     strip       replace           split          number 100000    0 12935059100027502   I was disappointed to see what I considered the method with the worst readability was the method with the best performance    there are tradeoffs to consider when going with the most readable option    for the type of workloads I use python for I usually value readability over a slightly more performant option  but as usual it depends

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To further complete  Ryan  s answer using json  one very convenient function to convert unicode is the one posted here  https   stackoverflow com a 13105359 7599285  ex with double or single quotes    gt print byteify json loads u    A   B   C      D      gt print byteify json loads u    A   B   C      D    replace               A    B    C     D     A    B    C     D

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So  following all the answers I decided to time the most common methods   from time import time import re import json   my str   str list range 19    print my str   reps   100000  start   time   for i in range 0  reps       re findall   w    my str  print  Regex method  t    time   - start    reps   start   time   for i in range 0  reps       json loads my str  print  json method  t    time   - start    reps   start   time   for i in range 0  reps       ast literal eval my str  print  ast method  t t    time   - start    reps   start   time   for i in range 0  reps        n strip   for n in my str  print  strip method  t    time   - start    reps         regex method     6 391477584838867e-07     json method      2 535374164581299e-06     ast method       2 4425282478332518e-05     strip method     4 983267784118653e-06   So in the end regex wins

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you can save yourself the  strip   fcn by just slicing off the first and last characters from the string representation of the list  see third line below    gt  gt  gt  mylist  1 2 3 4 5  baloney   alfalfa    gt  gt  gt  strlist str mylist    1     2     3     4     5      baloney       alfalfa     gt  gt  gt  mylistfromstring  strlist 1 -1  split         gt  gt  gt  mylistfromstring 3   4   gt  gt  gt  for entry in mylistfromstring          print entry          type entry       1  lt class  str  gt  2  lt class  str  gt  3  lt class  str  gt  4  lt class  str  gt  5  lt class  str  gt   baloney   lt class  str  gt   alfalfa   lt class  str  gt

[python] How to convert string representation of list to a list?

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