How to frame two for loops in list comprehension python

Question

I have two lists as below  tags    u man   u you   u are   u awesome   entries     u man   u thats     u right  u awesome      I want to extract entries from entries when they are in tags   result       for tag in tags      for entry in entries          if tag in entry              result extend entry    How can I write the two loops as a single line list comprehension

User · Answer

tags    u man   u you   u are   u awesome   entries     u man   u thats     u right  u awesome     result       result extend entry  for tag in tags for entry in entries if tag in entry   print result    Output     man    thats    right    awesome

User · Answer

The appropriate LC would be   entry for tag in tags for entry in entries if tag in entry    The order of the loops in the LC is similar to the ones in nested loops  the if statements go to the end and the conditional expressions go in the beginning  something like   a if a else b for a in sequence    See the Demo -    gt  gt  gt  tags    u man   u you   u are   u awesome    gt  gt  gt  entries     u man   u thats     u right  u awesome     gt  gt  gt   entry for tag in tags for entry in entries if tag in entry    u man   u thats     u right   u awesome     gt  gt  gt  result          for tag in tags          for entry in entries              if tag in entry                  result append entry     gt  gt  gt  result   u man   u thats     u right   u awesome      EDIT - Since  you need the result to be flattened  you could use a similar list comprehension and then flatten the results    gt  gt  gt  result    entry for tag in tags for entry in entries if tag in entry   gt  gt  gt  from itertools import chain  gt  gt  gt  list chain from iterable result    u man   u thats   u right   u awesome     Adding this together  you could just do   gt  gt  gt  list chain from iterable entry for tag in tags for entry in entries if tag in entry    u man   u thats   u right   u awesome     You use a generator expression here instead of a list comprehension   Perfectly matches the 79 character limit too  without the list call

User · Answer

In comprehension  the nested lists iteration should follow the same order than the equivalent imbricated for loops   To understand  we will take a simple example from NLP  You want to create a list of all words from a list of sentences where each sentence is a list of words    gt  gt  gt  list of sentences      The   cat   chases    the    mouse         The   dog   barks         gt  gt  gt  all words    word for sentence in list of sentences for word in sentence   gt  gt  gt  all words   The    cat    chases    the    mouse         The    dog    barks          To remove the repeated words  you can use a set    instead of a list       gt  gt  gt  all unique words   list  word for sentence in list of sentences for word in sentence    gt  gt  gt  all unique words        dog    the    chase    barks    mouse    The    cat     or apply list set all words     gt  gt  gt  all unique words   list set all words          dog    the    chases    barks    mouse    The    cat

User · Answer

This should do it    entry for tag in tags for entry in entries if tag in entry

User · Answer

The best way to remember this is that the order of for loop inside the list comprehension is based on the order in which they appear in traditional loop approach  Outer most loop comes first  and then the inner loops subsequently   So  the equivalent list comprehension would be    entry for tag in tags for entry in entries if tag in entry    In general  if-else statement comes before the first for loop  and if you have just an if statement  it will come at the end  For e g  if you would like to add an empty list  if tag is not in entry  you would do it like this    entry if tag in entry else    for tag in tags for entry in entries

User · Answer

return  entry for tag in tags for entry in entries if tag in entry for entry in entry

[python] How to frame two for loops in list comprehension python

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