Gather generates invalid Python code in simple scenario.

[greazer]

To repro with gather extension:

1) Open a notebook with these two cells:

#%%
A = [0,1,2,3]
B = [4,5,6,7]
sum = 0
diff_sum = 0
for i in range(min(len(A), len(B))):
    sum += A[i] + B[i]
    diff_sum += A[i] - B[i]

#%%
print(sum)

2) Execute the first cell twice. 3) Execute the second cell. 4) Gather the second cell to a new notebook.

Expected: 2 cells

#%%
A = [0,1,2,3]
B = [4,5,6,7]
sum = 0
for i in range(min(len(A), len(B))):
    sum += A[i] + B[i]

#%%
print(sum)

Actual: 3 cells

#%%
A = [0,1,2,3]
B = [4,5,6,7]
for i in range(min(len(A), len(B))):

#%%
A = [0,1,2,3]
B = [4,5,6,7]
sum = 0
for i in range(min(len(A), len(B))):
    sum += A[i] + B[i]

#%%
print(sum)

The first cell is invalid Python code and shouldn't be included in the final gather.

[greazer]

Does not repro using version 0.2.0 of python-program-analysis.