execution order of expressions in a list comprehensions [duplicate]

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Understanding nested list comprehension

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Given the following expressions:

matrix = [[1,2,3],[4,5,6],[7,8,9]]

A matrix is created, then a list comprehension is executed to create a flat list. The comprehension runs from left to right.

flat = [x for row in matrix for x in row]

Subsequently for each row in the matrix its values are squared. How is this comprehension evaluated?

squared = [[x**2 for x in row] for row in matrix]

edited Nov 21 at 19:55

timgeb

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asked Nov 21 at 19:49

dcrearer

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marked as duplicate by roganjosh, juanpa.arrivillaga python
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Nov 21 at 20:01

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

let me review that post... thanks for the reference
– dcrearer
Nov 21 at 19:54

add a comment |

up vote
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down vote

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This question already has an answer here:

Understanding nested list comprehension

2 answers

Given the following expressions:

matrix = [[1,2,3],[4,5,6],[7,8,9]]

A matrix is created, then a list comprehension is executed to create a flat list. The comprehension runs from left to right.

flat = [x for row in matrix for x in row]

Subsequently for each row in the matrix its values are squared. How is this comprehension evaluated?

squared = [[x**2 for x in row] for row in matrix]

edited Nov 21 at 19:55

timgeb

47.6k116288

asked Nov 21 at 19:49

dcrearer

6492726

marked as duplicate by roganjosh, juanpa.arrivillaga python
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Nov 21 at 20:01

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

let me review that post... thanks for the reference
– dcrearer
Nov 21 at 19:54

add a comment |

up vote
0
down vote

favorite

This question already has an answer here:

Understanding nested list comprehension

2 answers

Given the following expressions:

matrix = [[1,2,3],[4,5,6],[7,8,9]]

A matrix is created, then a list comprehension is executed to create a flat list. The comprehension runs from left to right.

flat = [x for row in matrix for x in row]

Subsequently for each row in the matrix its values are squared. How is this comprehension evaluated?

squared = [[x**2 for x in row] for row in matrix]

edited Nov 21 at 19:55

timgeb

47.6k116288

asked Nov 21 at 19:49

dcrearer

6492726

This question already has an answer here:

Understanding nested list comprehension

2 answers

Given the following expressions:

matrix = [[1,2,3],[4,5,6],[7,8,9]]

A matrix is created, then a list comprehension is executed to create a flat list. The comprehension runs from left to right.

flat = [x for row in matrix for x in row]

Subsequently for each row in the matrix its values are squared. How is this comprehension evaluated?

squared = [[x**2 for x in row] for row in matrix]

This question already has an answer here:

Understanding nested list comprehension

2 answers

python list list-comprehension

edited Nov 21 at 19:55

timgeb

47.6k116288

asked Nov 21 at 19:49

dcrearer

6492726

edited Nov 21 at 19:55

timgeb

47.6k116288

asked Nov 21 at 19:49

dcrearer

6492726

edited Nov 21 at 19:55

timgeb

47.6k116288

edited Nov 21 at 19:55

timgeb

47.6k116288

edited Nov 21 at 19:55

timgeb

47.6k116288

asked Nov 21 at 19:49

dcrearer

6492726

asked Nov 21 at 19:49

dcrearer

6492726

asked Nov 21 at 19:49

dcrearer

6492726

marked as duplicate by roganjosh, juanpa.arrivillaga python
Users with the python badge can single-handedly close python questions as duplicates and reopen them as needed.

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Nov 21 at 20:01

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

marked as duplicate by roganjosh, juanpa.arrivillaga python
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Nov 21 at 20:01

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

let me review that post... thanks for the reference
– dcrearer
Nov 21 at 19:54

add a comment |

let me review that post... thanks for the reference
– dcrearer
Nov 21 at 19:54

let me review that post... thanks for the reference
– dcrearer
Nov 21 at 19:54

add a comment |

1 Answer
1

active

oldest

votes

up vote
0
down vote

accepted

The first comprehension is equivalent to:

flat = 

for row in matrix:

    for x in row:

        flat.append(x)

The second comprehension is equivalent to:

squared = 

for row in matrix:

    tmp = 

    for x in row:

        tmp.append(x**2)

    squared.append(tmp)

(Except for creating additional variables in the enclosing scope like x, row, tmp.)

edited Nov 21 at 20:17

answered Nov 21 at 19:53

timgeb

47.6k116288

1

thanks for the clear concise sample...
– dcrearer
Nov 21 at 19:57

@wim right, I overlooked those. The del-ing is probably unnecessary to get the point across.
– timgeb
Nov 21 at 20:17

add a comment |

1 Answer
1

active

oldest

votes

1 Answer
1

active

oldest

votes

up vote
0
down vote

accepted

The first comprehension is equivalent to:

flat = 

for row in matrix:

    for x in row:

        flat.append(x)

The second comprehension is equivalent to:

squared = 

for row in matrix:

    tmp = 

    for x in row:

        tmp.append(x**2)

    squared.append(tmp)

(Except for creating additional variables in the enclosing scope like x, row, tmp.)

edited Nov 21 at 20:17

answered Nov 21 at 19:53

timgeb

47.6k116288

1

thanks for the clear concise sample...
– dcrearer
Nov 21 at 19:57

@wim right, I overlooked those. The del-ing is probably unnecessary to get the point across.
– timgeb
Nov 21 at 20:17

add a comment |

up vote
0
down vote

accepted

The first comprehension is equivalent to:

flat = 

for row in matrix:

    for x in row:

        flat.append(x)

The second comprehension is equivalent to:

squared = 

for row in matrix:

    tmp = 

    for x in row:

        tmp.append(x**2)

    squared.append(tmp)

(Except for creating additional variables in the enclosing scope like x, row, tmp.)

edited Nov 21 at 20:17

answered Nov 21 at 19:53

timgeb

47.6k116288

1

thanks for the clear concise sample...
– dcrearer
Nov 21 at 19:57

@wim right, I overlooked those. The del-ing is probably unnecessary to get the point across.
– timgeb
Nov 21 at 20:17

add a comment |

up vote
0
down vote

accepted

The first comprehension is equivalent to:

flat = 

for row in matrix:

    for x in row:

        flat.append(x)

The second comprehension is equivalent to:

squared = 

for row in matrix:

    tmp = 

    for x in row:

        tmp.append(x**2)

    squared.append(tmp)

(Except for creating additional variables in the enclosing scope like x, row, tmp.)

edited Nov 21 at 20:17

answered Nov 21 at 19:53

timgeb

47.6k116288

The first comprehension is equivalent to:

flat = 

for row in matrix:

    for x in row:

        flat.append(x)

The second comprehension is equivalent to:

squared = 

for row in matrix:

    tmp = 

    for x in row:

        tmp.append(x**2)

    squared.append(tmp)

(Except for creating additional variables in the enclosing scope like x, row, tmp.)

edited Nov 21 at 20:17

answered Nov 21 at 19:53

timgeb

47.6k116288

edited Nov 21 at 20:17

answered Nov 21 at 19:53

timgeb

47.6k116288

answered Nov 21 at 19:53

timgeb

47.6k116288

answered Nov 21 at 19:53

timgeb

47.6k116288

1

thanks for the clear concise sample...
– dcrearer
Nov 21 at 19:57

@wim right, I overlooked those. The del-ing is probably unnecessary to get the point across.
– timgeb
Nov 21 at 20:17

add a comment |

1

thanks for the clear concise sample...
– dcrearer
Nov 21 at 19:57

@wim right, I overlooked those. The del-ing is probably unnecessary to get the point across.
– timgeb
Nov 21 at 20:17

thanks for the clear concise sample...
– dcrearer
Nov 21 at 19:57

@wim right, I overlooked those. The del-ing is probably unnecessary to get the point across.
– timgeb
Nov 21 at 20:17

add a comment |

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